Definitely nothing wrong with it and if anything learning other songs will enhance your creativity. Like others have said, there is alot to learn when playing someone else's song. As long as you don't copy it note for note your fine. If your worried about your creativity suffering, try writting original stuff and learning other's stuff also. Sometimes after learning a new tune, I find it easier to write something of my own later.

If there's something you like, learn how to play it. :)