Have you washed or gotten the bike very wet recently? This happened to Wendy's bike once after washing it and got water under the sending unit boot. Could also be a bad sending unit. Are you sure the bike has pressure? This is the situation that prompted me to make an oil pressure gauge for our bikes. That way if the light came on again I have a mechanical gauge to verify pressure or no pressure.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!