I have a 1996 dodge ram 1500 and ABS brake light won't shut off even though the park brake isn't engaged could that be the ABS sensor need to be changed ?

No, the problem may be more serious than that. You need to have an ABS Code Reader attached to the under dash data link connector, in order to read the stored codes. Based on the codes, certain repairs likely need to be made. If you are lucky, it may mean just removing the ABS sensors (Torx E8) on each wheel and cleaning them with a spritzled rag. There are many other possibilities, however.

One of the best and cheapest defenses, to prevent expensive ABS repairs, is to change the brake fluid every 2 years with an ABS-approved fluid. This prevents internal corrosion from developing and damaging the modulator, internal pump, calipers, and other components.

My father failed to change the brake fluid regularly on his Camry. It took Toyota two weeks, and cost over $2,000, to repair the ABS system and replace pads and disks. He picked the car up today.

When we went to the mechanic he told us the sensor was loose but I don't think he ever fixed it

Each wheel sensor is mounted with an E8 Torx bolt, after a small amount of thread locker is applied. That should be an easy fix, if that's all it is. Buy a small external Torx socket set and you should be able to fix it yourself. Access should be easy.