The man was found by a search and rescue team on Wednesday night and taken to a field hospital in the city, State radio reported on Thursday.
"When he arrived at the hospital his signs of life were very weak. He was frozen and now he is in a coma," said medic Mehdi Shadnoush, part of a Ukrainian-Iranian medical team treating the man at a field hospital in the quake-ravaged city.
The man lay on a hospital bed covered by a white blanket and had an oxygen mask over his mouth and nose. He looked very thin and had a white-and-black beard.
"We are following his status minute by minute," Shadnoush told Reuters.
He was the first survivor to emerge alive from the ruins of
the ancient Silk Road City 1000 km southeast of Tehran since a woman in her 90s was rescued on 3 January.
Experts say it is very rare for people to survive for more than 72 hours in such conditions.
A 97-year-old Iranian woman
was pulled out alive on Saturday
The man was unable to speak, the radio said. Aid workers said the rescued man, whose first name is thought to be Jalil, had travelled from a nearby village to stay with his sister in Bam the night before the earthquake struck.
"We have sent people to his village to bring his wife to the hospital," said Iranian aid worker Muhammad Riza Tahmasbi.
At least 30,000 people were killed by the earthquake in Bam, an ancient Silk Road city in southeastern Iran. Ninety percent of its buildings were also ruined.
New Major alert
Meanwhile Iran went back to a major alert over the possibility of a deadly earthquake on Wednesday. A day later two tremors hit a major oil- and gas-producing area in southwest Iran, seismologists said.
The latest tremors, in the Masjed Soleiman area, bring to 30 the number recorded in two days, said scientists at Tehran university's geophysical institute quoted by state news agency IRNA.
The Bam quake has also prompted the Islamic republic's clerical leaders to consider proposals to shift the political capital out of quake-prone Tehran, which sits on several major seismic faultlines.