Bugeye

okay so i was driving my 03 S the other day on the interstate when the abs light popped up. brakes still felt fine and they work just like they always have. well the next day i had an autocross scheduled and learned for a fact that the abs was not on lol. brakes still felt normal but the ABS was not working.
every now and then, and it seems like it happens right after startup, like as im leaving a parking lot or my driveway, i will go to push in the brake pedal (while traveling at a slow speed obviously) and the pedal almost seems like its pulsing, kind of like the same way it feels when the abs kicks in while driving on snow is the only way i know how to describe it. the car still stops just fine and it only does that like once a week, but i would like to know how to fix it, or at least what to look for. replaced brake pads about 5k miles before this started happening and everything seemed fine. anyone have any ideas? going to check the fluid when i get out of class today.