Yes. After fermentation there is a lot of CO2 dissolved in the beer and it will slowly leak out. Also, if the room is slowly warming the air in the headspace will expand and that will also cause bubbling. At 12 days, it really should be done. But you only need FG readings to see if it is done (take 2 a few days apart and see if it changes). If they are the same and it tastes good, bottle it up.