Following the report of a fire beneath the right wing by a passenger and an inconclusive inspection by CFR; an A320 returned to the gate for a maintenance inspection. No evidence of fire was found.

Narrative

While taxiing for takeoff we received call from a Flight Attendant stating that a passenger was reporting that the wing was on fire. The Flight Attendant said she didn't see anything; but that she was not in a good position to see it without moving passengers. I asked her to move the passengers and look. We notified the Tower and asked for the fire trucks. We had no abnormal indications in the flight deck. The Flight Attendant called back and said she saw nothing; but that at least two passengers had witnessed flames under the right wing.I made a PA to the passengers to alert them that we had the fire trucks approaching the aircraft to inspect a possible problem. The Fire Department reported no fire and took a heat signature of the aircraft. They reported that all looked normal with some smoke near the number 2 engine. We decided it would be best to go back to the gate and have Maintenance inspect the aircraft.When we arrived at the gate one of the passengers came forward to explain what she saw. Her description was consistent with engine torching. Maintenance came and inspected the engine and wing area; ran the engine and found no anomalies. The logbook was signed off and we continued with no further incident.