Is the oil level correct?
Do you mean the oil light is on when the engine is idling (engine running but foot off accelerator/gas pedal)?
If so then you have a problem, either poor quality/wrong type of oil in car,blocked oil pick-up, poor oil pump, badly worn engine or faulty oil pressure sensor.
If the car was OK before the head gasket was fixed I'd say bad oil or blockage.
gerry
May 2011