I have recently purchased the new mac pro and I saw the GPU option is not enable and only recognizes the CPU one, what is frustrating. Does anybody know how to enable the GPU option?
See this for details of how the GPU is used in After Effects:
Note that your card will be used for all of the GPU acceleration features but one---the ray-traced 3D renderer---which requires an Nvidia GPU. That is an obsolete feature that you don't need to worry about, anyway. There are many better alternatives to using 3D in After Effects, including Cinema 4D, which is now included with After Effects: