I've had this, usually it's because I temped at a different time (it's recommended to have a usual time to temp when you wake up, and try to be within 1/2 hr of either side of it). Perhaps you are unwell? Or maybe you're pg? and you're having a triphasic shift? (I think that's what it is called?)

Sorry, might not be all that helpful! LOL. If you find your temp is back down to a normal range tomorrow, you can probably discard that high temp.