AC Voltage: Fluctuation?

I've got a Monster Power HTS3500 (I know, its been covered ad nauseum) which has a voltmeter on the front. Granted, I really don't know much about electricity other than I pay the power company for it. Usually, it reads at 120 or 121 but this morning it was hovering around 125 or 126. Is this a large or unusual level? I'm guessing it isn't because the dial isn't pegged but couldn't help but wonder about it. Why does this happen and is it cause for concern?

...my local PSC(or PUC for others) a fluctuation of 10% is not abnormal as it is "overall load" dependent...higher(or lower) numbers for extended periods of time may be cause for concern...

jimHJJ(...FWIW...)