Somehow missed this thread - life gets in the way of a good time, sometimes!
As the posts above indicate, this is Topps reverse art for the 1965 baseball set. Seems these small pieces were almost always done in a big sheet with multiple card backs, and as was mentioned, they are quite often cut down (by Topps or someone who got a full sheet) to small groups or individuals. I think the resale value is much higher in individual pieces, since team and player collectors will pay more individually for the art pieces they are interested in.
There was a recent thread on these here:
http://www.net54baseball.com/showthread.php?t=176503
I did see this one on the Bay a while back, and was interested at first, but then was a little sad to see that the Mantle artwork was not used on his card from that year. Still a really cool piece, and 1 of 1!