AJ, who moved to Crystal Palace as part of the deal that saw Clinton Morrison join Blues two seasons ago, rattled in four goals during the month of October.
Ironically, one of those October strikes came in his first appearance back at St Andrew's when Palace won by the only goal of the game.
Johnson has bagged eight goals so far this season making him the top scoring Englishman in the Premiership to date.
Meanwhile, Portsmouth manager Harry Redknapp picked up the Barclays manager of the month award.