Was traveling ~60mph on a 3 lane section of interstate highway when vehicle in front of me abrutly decreased speed. I braked until my vehicles matched that speed. As I raised my foot from the brake pedal (I had matched the speed of the vehicle in front of me and had an acceptable amount of seperation given the flow of traffic), the brake pedal fell away from my and to the floor and I felt ABS engage. This nearly resulted in my vehicle being rear ended by the car following me. I have driven with the emergency braking system active since the incident (as it is by default after every vehicle power cycle) and have not encountered this behavior again. This had not previously occured in the ~20,000 miles of usage prior to the incident. Since no damage occured during the incident, the vehicle has not been inspected by anyone besides myself.