Is there a particular reason to do this?
I've flashed BIOS via the internet before, but I would say that it can for a variety of reasons be catastrophic. If, for example, there is a power cut or a spike in the power supply, or if there is a glitch caused by some other software deciding to look for an update (virus checker, adobe 6, whatever) your update could be unsuccessful. In such a case you could be left with an inoperative motherboard
If you look on the motherboard manufacturer's site where the update is located you should be able to find details of what the update contains, and if it fixes a problem you have on your computer then the risk may be worthwhile. If not, then don't feel that you must update just for the hell of it, please leave it alone