Mubarak was moved out of prison to a military hospital after the 84-year-old suffered a stroke.
The state news agency MENA said Mubarak was "clinically dead" when he arrived at the hospital from prison, and said doctors used a defibrillator on his several times. MENA initially said the efforts were not successful.
But the official said Mubarak was put on life support. He had no further details on his condition.
Maj. Gen. Mohsen el-Fangari, a member of the ruling military council, told the Al-Shorouk newspaper website that Mubarak was in a "very critical condition," but denied he was dead. Mubarak's wife, Suzanne, came to the hospital, where Mubarak was in an intensive care unit, another security official said.
The news of Mubarak's health adds further layers to what is threatening to become a new chapter of unrest and political power struggles in Egypt, 16 months after Mubarak was ousted by a popular uprising demanding democracy.
The Associated Press contributed to this report.