An automatic "pull up" alarm went off when the plane, travelling from Malabo, the capital of Equatorial Guinea, to Douala, Cameroon's largest city on May 2, diverted from its normal route "to avoid storms," the BEA accident investigators said.
That manoeuvre had put it on course to hit the 4,040-metre (13,255-foot) Mount Cameroon, before the alarm prompted the pilots to swiftly gain altitude and miss the mountain.
No-one was injured and the plane continued its flight without further incident.
Air France confirmed the incident, saying that it would be carrying out its own internal inquiry.
"A route to avoid a storm brought the plane toward the side of Mount Cameroon," it said in a statement.
The EGPWS (enhanced ground proximity warning system) went off in the plane's cockpit and "the pilots to respond immediately by executing the appropriate manouevre," Air France added.