I have one computer that says 13 volts with Asus probe. It seems to run fine. You might want to use another monitor program to confirm the results. I'm not sure mine is accurate. My main computer says 11.8 volts. I've switched out my main computers power supply and got the same results with 13 volts. All I can think is the monitor program is off a little. I wouldn't be too worried about it.
If the actual voltage is 12.9 it could be a concern. Your fans and periphs will run a little above spec and wear out sooner though I wouldnt worry about things frying. If your 5v is high then you have to worry about your mobo and pci cards. Check it with a multimeter to be sure.