Amuscle with the opposite action of the prime mover is called

Antagonist muscles

Explanation:

A muscle with the opposite action of the prime mover is called an antagonist.

Agonist muscles are those that, during any movement, apply the force that allows the movement to occur. 

Antagonist muscles, on the other hand, are those that do not contract in any way during a movement. 

Antagonist muscles are simply the muscles that produce an opposing joint torque to the agonist muscles. This torque can aid in controlling a motion. The opposing torque can slow movement down.