My MIL does this all the time, though I've never had the need. Someone once said that it's fine to do, but you should sift the mix before you use it (breaks up any clods formed while freezing).
I freeze all my cakes. Just let them thaw in the fridge before you take off the saran wrap and foil.
Are you talking the box of mix or the baked cake?
Either way, it's fine.
The box mixes. They are having a sale on them & I wanted to get a few..
Sure you can. Go for it.