Mine did that at a stop sign, went right through the intersection. I only had 200 miles on my 4runner at the time. I thought my foot slipped of the pedal or something, but the pedal went to the floor and I pumped it and by that time I was already through the intersection. Took it to the dealer and could not get it to replicate for the service manager. So I kept on driving it. Year and a half later (20,000 miles) a small animal ran out in front of the 4runner, feeling generous I slammed on the brakes and the car pulled hard to the left and put me into the other lane. Took it to the dealer, they took the brakes apart and it turns out there was air in the lines close to the calipers (or something like that is what the service manager told me) I was a little pissed that I had been driving around with air in my brake lines...
so get your brakes checked!!!