KANDIE - hi, what you're describing should be the diverter. When you activate the shower mode, you pull up on a knob or lift some sort of handle, and that diverts the flow of water from the tub spout to the shower head. The gasket/washer in the diverter can go bad over time and allow some water to flow out of the tub spout at the same time the shower head is in use.
Fixing it can be easy to do - it depends on how you activate the diverter. Is the knob/handle located on the tub spout, either close to where the water comes out or close to where the spout mounts to the wall? If so, you can get a replacement spout at the big box home improvement stores (H-ome D-epot, L-owes). They also sell diverter repair kits but it's almost faster to simply replace the tub spout. It should easily be unscrewed from the pipe that comes through the wall. Take it with you to the store so you can get the right replacement. If you have the name of the fixture, e.g., Delta, Peerless, etc., take that with you and be able to describe it (e.g., 1 handle, pull out to turn on water flow, twist clockwise to change water temperature).
If the diverter handle is mounted elsewhere, e.g., inside the tub, then you may need to call in a plumber or a good handyman to accomplish the repairs. It may require getting access through the wall behind the fixture. I hope this helps you some - good luck! Jim D/West Point, VA