My car has been doing this lately also. The light will come on and off as it wants. It only seems to do this when the engine temp hasn't made it to the normal mark. I would suggest scanning your car for codes like everyone else has said. I have a friend with a scanner but I haven't made it to him yet.
Someone told me that scanners will only pick up codes when the engine light is on so you may want to try that. I had my car scanned a while ago when the light wasn't on and it still found codes so who knows. If I find my friend and we come up with codes for my car I'll come back here and post what we found.