An Egyptian-led team said on Saturday that the information was found on a cockpit flight recording.
But the investigative committee said it was too early to say where or why the fire broke out.
All 66 people on board died when flight MS804, flying from Paris to Cairo, crashed on 19 May.
The new information appears to back up evidence from the flight recorder of smoke in the cabin.
Recovered wreckage also showed signs of high temperature damage and soot on the jet's front section.
Automated electronic messages sent out by the plane had shown smoke detectors going off in a toilet and in the avionics area below the cockpit, minutes before the plane disappeared.
No distress call was made from the plane prior to the crash.
Egyptian investigators have not ruled out any reasons for the crash, including terrorism, particularly as such catastrophic fires on passenger planes are so rare.
The data recorders were taken to Paris after being found, and the cockpit voice recorder was in need of considerable repair.
The investigative committee also said on Saturday that a research ship, the John Lethbridge, had finished its search for human remains, which have been transferred to Cairo for identification.
An audio recording made on board an EgyptAir flight that crashed in the Mediterranean Sea in May discusses a fire, investigators say.