No, Selena Gomez has never posed naked.
However, there has been some fuss and rumours going around... especially after a picture of Selena Gomez came out revealing her as a cover for Playboy in March 2013.
This picture was a fake though and even if she was offered money to do a photo shoot with the magazine, she didn't accept. So, the picture was only an art piece submitted by a fan.
The only pictures of her that might seem more "provocative" are the ones taken from the movie "Spring Break" that came out in 2013. If you want to have a look, here's the trailer:
Hope this helps!