Has any herbicide been sprayed nearby recently? That is one possible cause. Another is worse news -- it could be Rose Rosette Virus (RRV), which would be fatal for the rose. If the stems with these weird leaves look extra thorny and/or thick, that's another bad sign toward RRV -- but I can't see it in this pic. Google "Rose Rosette Virus" for images and compare it to your rose. Be aware that many roses have reddish new growth, so don't go by color alone. Look at the other characteristics.

:-/

~Christopher

Please post more views of the aberrant growth.

And tell us, please, where you are located.

Jeri