ahh no need to worry at all, sounds like you have a happy betta :D . all he is doing is making a bubble nest. Whenever bettas are happy they blow bubbles in the corner of the tank, that way whenever a female comes around (this is in nature of course) to mate, he can pick up the eggs with his mouth and spit them on top of the bubbles.
There are always bubbles at the surface in a betta tank if the betta is happy and is at the right temperature. If you see a large pile of bubbles maybe 3 or 4 bubbles thick and spread over a several square inch area, you have a very ready male that would enjoy some company for only a few hours. After that, the female would need another tank to get away from him.