A CEL can be caused by many things, usually a loose gas cap or defective sensor.
Maybe someone has been messing with your gas cap.
Loosen and tighten it a couple of times. Then go for a test drive to a "easy" entrance/exit auto supply (Autozone, O'Rilley, etc) where they will help you scan for OBD-ll codes.
If the code was caused by a loose cap it might be cleared by the time you get there