Basically, what Ruffinit said. You should determine if the ABS is activating because one of the wheels locking up, or is it activating for no obvious reason.

If it's activating because a wheel is actually locked up, then you probably have some mechanical problem with your recent brake installation and you need to investigate that. I'm guessing that the problem is in the rear, since those wheels have little weight on them and will lock up much easier.

If it's activating even tho no wheel is locking up, then it's probably a sensor problem and you need to investigate that.

If it's a business that did the brake job, then you should probably return to them for remedial work. It sounds as if the problem is the result of that work.