If your mechanic has the time, you can ask them to check at the ABS Wheel Speed Sensor. It is located within the Brake Rotor 'hat' and as you can imagine, will take some time and work to take out.
Most of the time, it just needs cleaning but be careful, as the plastic casing may be brittle.
This will just be Labor costs to you, but if you can do it yourself, hey, all the better!
In any case, if it doesn't work, then as Tech said, look at the ABS Modulator.
Where are you in Malaysia? Since you are from Malaysia, try to check with the mechanic and try get a rebuild one. A rebuilt version should cost less than RM500 only. If you were quoted more, then they are trying to make a quick buck.