2003 Ford Mustang Burning smell/ smoking

I was driving earlier and smelled a burning smell so I pulled over and popped my hood and on the left side of the engine by the intake filter where the belt is, it's the first ring where the belt goes around that's closer to the intake filter, and from the back side of the belt was smoking, not a lot but you could definitely see it, I waited for a few mins then it had stopped j waited about 10 mins before I started my car again to see if it would start smoking again & it didn't. But what could be the cause of this??