I got a similar issue with my drivers door. Does yours lock with the rest of the car?
Mine only locks by having to push the button down so I have to clime across the passenger side to open it and lock it. Mine is the actuator which I need to replace when the weather gets better as I need to strip the door.
Could also be the lock module itself though have a search there are tons of threads about the door locks they seem to be a big problem!