Sure, it's possible for co2 to continue to off-gas after fermentation is over. That's perfectly normal.
If you want to see it really go crazy, take it from a cooler place to a warmer place! When I have some ales cold conditioning a bit after fermentation, and I bring them out to the kitchen to get ready to keg or bottle, the airlock goes crazy! The reason is simply that cooler liquids "hold" co2 better, and when I move it to a warmer place, it bubbles quite a bit as the co2 is released.
Temperature changes and weather changes (like a rise in barometric pressure) can cause this, and so can moving the fermenter.