ABS - lights

I have a 1995 monte carlo z34 which the ABS light intermittently comes on and when I turn the car off, start it later on, the light goes off, but meanwhile I never know if I really have a problem with my brakes or not. A couple of times now, my anti brake light and the brake light came on and stayed on at start up, until I got home. Is there any known problem that I should have concern with? or be able to tell the mechanic about? Because I do take it to a chevy dealer and so far they have replaced the ABS pump and say they can not find anything else wrong. yet this light goes on at it's own will.