The 23-year-old is on loan at the League One club and was involved in an unsavoury incident in their recent game against Peterborough.
O'Hara is alleged to have bitten an opponent during the game, and could face disciplinary action as a result.
The 1-1 draw was marred by the incident on the 44th minute, when O'Hara bit Sam Szmodics.
He has until March 6th to respond to a violent conduct charge.
He did not get a punishment during the game, as the referee may have missed the incident in real time.