Normal Mutants are one of the most common enemies in the game, and they don't pose much of a threat, unless there are a lot of them.
The normal mutant will just run toward the player and lunge when it gets close, attacking with its hands. West will be slowed for a second if this attack lands (unless his shield blocks it). You can avoid its attacks by strafing, or by pressing space bar to dash away from their attacks. Normal mutants are only remotely dangerous in numbers, but they can still be outrun easily.