This is an all too common problem.  I had it happen to my Chrysler, and my friends have had it happen to their Le Baron.   What we all had to do was to take it to the service department at our dealership.  For mine, something had to be reprogrammed, and it took about an hour.  I had made an appointment, and decided to wait for the car.  The service department manager said that there was a problem with a “chip” that controls when the air bag is deployed.  It was a good thing that the light was coming on at odd times.  If your air bag deploys when there is no impact or reason, someone could get injured.  My friend’s car had a problem that was more complicated.  They actually got a recall letter about this problem so there was no cost involved.  Definitely get it checked out, because it is probably something that will be under warranty.