Six weeks is a very long time for yeast to be active in a beer. You either have outgassing due to a low pressure system coming through or warming of the beer, or you have something other than yeast active in there. Or perhaps you had the beer much too cold during fermentation and the yeast are just waking up again.
Take a gravity reading to see if it has hit FG, and take a taste to see if the flavor is right.
