ABS system

When turn on ignition switch, the ABS on dashboard comes on and goes off after few seconds as normal.

My problem is the ABS again comes on and stays in dash when the car starts to move (speed reaches about 5 km/h).

I have taken few steps as follows:

1. Checked all fuses for ABS (03 nos.-01 under dash and 02 on engine compartment) and they are good.

2. Lift up 04 wheels one at a time and rotate by hand When the ignition on position, the ABS comes on either of rear wheels but not for any of front wheels.

3. Therefore I have cleaned 02 rear wheel sensors and the toothed wheel but there was nothing on them (no dirt or dust).

The Problem still exists and expecting your valuable advice to rectify this problem.