In ancient Egypt, an evil sorcerer named Scarab kills the pharaoh's son, Prince Rapses, to become immortal. Entombed alive for his crime, Scarab revives in the modern world and begins his search for Rapses' reincarnation, a San Francisco-dwelling boy named Presley Carnarvon, to retrieve the spirit of Rapses so he can become immortal. Rapses' (Presley's) bodyguards, Ja-Kal, Rath, Armon, and Nefer-Tina, along with Rapses' cat, Kahti, awake from the dead to protect him from Scarab. They use the power of Ra to transform into powerful guardians.

Each of the mummies is aligned with the power of an Egyptian god. Ja-Kal uses the spirit of a falcon, Rath uses the spirit of a snake, Armon uses the spirit of a ram, and Nefer-Tina uses the spirit of a cat. The mummies are able to call upon it for magical armor and powers to fight superhuman evildoers by shouting "With the strength of Ra!". Once their strength is exhausted, they must rest in their sarcophagi to regain the ability. The mummies also have the power to make a horrifying face, usually used to scare away nosy bystanders.

In addition to Scarab, the mummies often had to contend with gods and spirits from Egyptian myth summoned to the modern world, including Anubis, Set, Geb, Apep, Bast, Sekhmet, Bes, and many others, usually as part of one of Scarab's schemes that went out of his control.

• Presley Carnovan – voiced by Bill Switzer: A 12-year-old boy who has the spirit of Prince Rapses XII (an ancient pharaoh) who is based on Ramses. He soon discovers this when the Mummies introduce themselves as his guardians. He lives in San Francisco with his mother. He is reluctant to accept his role as Rapses, but on at least two occasions where he had the chance to be freed of his role, he expressed reluctance at losing his status as "Pharaoh" because it would have also meant him losing the mummies.
• Prince Rapses: He was the heir to the Egyptian throne 3500 years ago. He was protected by the Mummies (before they were Mummies) but was killed when he was Presley's age by Scarab. His spirit now lies within Presley, and is drawn out by Scarab in several episodes. Rapses himself comes to the present in "The Prince and the Presley", when Scarab steals a time travel scroll to draw him to the present in the hopes that he would be easier to capture than the present Presley. Rapses returns to the past at the end of the episode.
• Amanda Carnovan – voiced by Louise Vallance: Presley's mother. She works at the City Museum. In "Ghouls' Gold", Armon refers to her as "the wise Amanda" when recalling advice she gave Presley. She has insecure feelings that Presley misses being with his father, who is away on business, and tries to bond with her son often, such as taking him out camping, as she desperately tries to fulfill both the role of a father and a mother.
• Ja-Kal – voiced by Dale Wilson: The leader of the Mummies, in his transformed state, his armor resembles a falcon and it also allows him to fly. His weapon are his razor sharp talons/claws and a bow that can shoot out flaming arrows. In ancient Egypt, Ja-Kal was a hunter who had a wife named Tia and a newborn son named Padjet; he died without knowing what happened to his family. He worries the most of Presley's safety, often acting as a father-figure to him. He commonly uses hunting terms to talk to others and explain situations. Ja-Kal commonly cares for other people's needs first and himself second. In "Family Feud: Part 2 – New Mummy in Town", it was revealed that he had a brother, Arakh, who was a notorious bandit.
• Rath – voiced by Scott McNeil: The most intelligent of the Mummies, and also the only one able to cast spells. When he transforms, a green snake which turns into a golden cobra wraps around him and serves as his armor. His weapon of choice is a sword that can transform into a snake, but he is also able to perform magical incantations. He also designed and built the Mummies' vehicles. In the past, he served as the young Prince's tutor. He claims to know about science, but his definition is such things as turning a staff into a serpent, although he has learned to adapt some spells to the present (such as a spell that summoned underground snakes to bind his enemies in the past, but now summons electric cables in the present). Though they are enemies, Scarab does respect him for his spellcasting skills.
• Armon – voiced by Graeme Kingston: Armon is huge and eats very often. He is very strong even when not transformed. He lost his right arm fighting in the Pharaoh's army, and when he transforms has a golden arm that is used as his weapon. His armor resembles a ram. While not fighting, Armon spends most of his time eating or watching "the magic box" TV that Presley gave them. In the past, Armon was Rapses' teacher of combat.

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Originally, Mummies Alive! was geared towards an older audience, but during production, it became predominantly a children's show. The series ran for one season of 42 episodes; the last two episodes link together to end the show, as it appears episodes 38–40 were the finale of the first season. A second season was planned, but due to low ratings, it was canceled.

Eric and Julia Lewald, writers/producers for Mummies Alive!, were also head writers for the third season of the Gargoyles animated series. The programs share common plot elements, including a group of warriors from the past that awaken in the present to fight a wealthy, immortality-obsessed enemy; their initial difficulties in adapting to the modern world; the use of mythological figures in numerous episodes; and a recurring femme fatale antagonist. These similarities made Mummies Alive! vulnerable to criticism describing it as little more than a Gargoyles clone.