I've had a similar issue.
Firstly you need to get a dianostic scan carried out to see what fault codes are present.
For me it was the front nearside wheel speed sensor showing at fault but following a replacement sensor-no change, followed by a replacement ABS loom-no change, a replacement upgraded green brake pedal switch (just in case as its a known part to go wrong although brake lights were fine)-no change, now as a last resort i have bought a new hub which has the ABS pick up attatched and will be fitting soon-fingers crossed.
Oh fuse was also checked and fault code reset after each attempted fix, which reset fine each time only to beep three times and reappear as soon as i exceed 10mph.
Hope you have an easier fix and this goes to show that fault codes can only tell you so much and although i have still been using the car and it is still driving fine it has been a pain but this needs to be your first step.
Good luck.