That file exists on my system, and I bought it as a motherboard and processor.
Maybe your motherboard BIOS came with a Windows licence? I don't know all the ways it can get embedded there.
Either way, if you start the installation, it'll never ask you for a key and you'll find everything's authorized automatically. Some machines (like this HP laptop) have very obvious OEM licenses (the string "OEM" shows up several times in the BIOS record) that probably wouldn't transfer well to VirtualBox, etc.
cheers,
Stewart