Are you curious if it's normal for the antilock brakes to work when braking in low traction conditions? If that's it, then yes, that's perfectly normal and expected, and indeed why the system exists. It's doing its job and keeping you from skidding due to locking the wheels. It's also a good indication that you might be well served by slowing down a little in those conditions and giving yourself even more room to brake and maneuver.
If you mean the ABS idiot light came on, that generally indicates some problem with the system, and diagnosing it pretty much requires as a first step reading the codes recorded with a code reader.
I know for myself that there are plenty of times when I've thought there was better traction, based on general appearances, than there was and probably should have adjusted my driving a little sooner than I did. Thankfully none of these has ended in any serious trouble as yet. Rain just starting is one case that can make for surprisingly slippery roads, as the water lifts the accumulated oily gunk but hasn't yet washed it all off. Leaves, particularly wet leaves, are another that can readily fool people.