My '91 used to do that right after an oil change. I never did figure out why and it quit doing it after a while. I never pulled codes to see what it was either. The car never ran bad or got bad mileage, the light just flickered.
If I had to do it all over again (or if it ever starts happening again), I'd do a code scan to see if it stored a code when it lit the light and go from there.