If you've installed Yosemite, you will need a newer CUDA version than our currently recommended 6.0.37. I would suggest installing the current 6.5.18 version.
You can see what version you have in Mac System Prefs, CUDA. There is an update button in the CUDA window. Even though it will say your current version needs to be updated, the update button will be grayed out and say no new version available, if your system behaves the same as other systems.
So you'll need to download CUDA from the NVIDIA driver download site here:
http://www.nvidia.com/object/mac-driver-archive.htmlWhen you try to install it, OSX won't let you, and you'll need to go to Mac System Prefs / Security and Privacy to sort that out.