Safe way, maybe. Computer cases have a basic purpose, that's to hold your computer, keep things from interacting haphazardly with the components, and also to look nice. You could in theory do the same by putting it a plain old box, I'd assume a cardboard or wood box would work fine. Once upon a time, I had to do without a case for a little while, I just put the motherboard flat on my desk and ran it. Nothing bad happened, but obviously the danger is something shorting out or hitting the board and damaging it.