you serious?
You can generally expect a up to 5% fluctuation, meaning 5% is towards the end where you don't want to be at, because at that point the lines is being taxed too much.
5% of 12 would be .6 so that'd be 12.6 or 11.4
It would raise a flag for me, buuuut I suppose if you aren't noticing any major stability issues then it could be something as simple as the voltages being read wrong.
Is that through BIOS or monitoring software or both?