First of, your terminology is very wrong (BIOS update for CPU??), you mean for the motherboard (as it doesn't make sense otherwise!)
Anyhow, BIOS updates should only be downloaded from the manufacturer site (and for the specific motherboard model)
If you've downloaded it from some 3rd party site, or for the wrong model, then this isn't surprising.
You should also always follow the instructions the manufacturer provides.
Anyways, why exactly do you need to update it if I may ask? The key role of BIOS updates is to add compatibility for newer CPUs, and enhance compatibility with various memory modules. If you have no valid reason to update the BIOS, then you shouldn't even attempt it (as there's a risk involved here, and you could potentially make the motherboard unusable if things go badly!)