When shifting the transmission into reverse the RPMs shoot up?

This is a problem that has started happening within the last month or so and it only happens intermittently but what happens is I’ll start the car and when I shift it into reverse the RPMs shoot way up and I have almost hammer the brake pedal to the floor but as soon as I shift it into neutral or drive it goes right back to normal and I cannot figure it out for the life of me. So, any thoughts or suggestions you can share would be greatly appreciated.