Brake Warning Light

I have 2000 Ford Mustang GT with 46,000 miles on it. Recently I have noticed that if I press my brakes really hard or suddenly, the brake warning light will briefly come on, then turn off when i begin to release the brake. I do not have any obvious loss of braking power, but I need to know if this is a serious problem, or if its something that simply happens. I don't think its the ABS kicking in because then I think that the ABS light would come on instead of the brake warning light. Does anyone have any ideas? If it is the a faulty brake system, I want to take it in right away, as I drive on Houston freeways all the time.

Thanks!