Is there a free will to react in a dream?

Most of the time, considering you are unconscious at the momment, I'd probably say NO. Dreams are usually just your brain playing out thought patterns like a movie and sending the signal to the "screen" which if your visual cortex.

However, there are dreams of which you possess awareness called "Lucid Dreams" in which you KNOW you are dreaming. With those dreams, I think you have some control and free will to react.