Boot your computer, and enter the BIOS. To enter the BIOS on my own computer's Gigabyte GA-P67A-D3-B3 motherboard, I have to press the delete key when it boots (before the operating system starts). Different manufacturers set different keys for opening the BIOS.
Once you have entered the BIOS, press the F9 key. This will open a System Information page. From here, you will be able to find your motherboard's BIOS version.
The F9 option on Gigabyte motherboards is poorly documented; you'll notice that it isn't mentioned anywhere in the shortcut tab of the main BIOS page. But once you discover it, it's definitely the easiest way to check your motherboard's BIOS version.
SEE ALSO: How to check the BIOS version of a motherboard from Windows