If I recall correctly at one time every time you reload the game the AI gets a turn which could result in the AI getting many turns in one "turn" if multiple save/reloads occured prior to pressing end turn.
I know this was an issue at one time and I also know that there was a change put in DA v1.6 to address this as evidenced by the change log.
+ TWEAK: Made a slight change to the code that starts the AI threads which may help with the AI seeming to get a free turn at the start of a new game or when loading a save game.
However I don't know for sure if this issue has been totally fixed or not.