There is one on RR12, in the small strip center next to Wake the Dead. I am sure there are others. They come and go and I don't keep track of them. It seems like there is one on Hopkins, just past the little HEB. I think it is a framing store and gallery, but I could be wrong about both.
If you just want to see art, as opposed to buying it, there is always the Wittliff Collection, in the library, on campus. There are regular student exhibitions on campus as well.
The Root Cellar and Wake the Dead have art displayed as well. That is generally for sale. I would bet Tantra and other local spots do as well.