Seems most likely that one of the sensors in the tires has gone bad. A tire shop should be able to figure out which one if any. (Using a hand held checker)
You didn't have your tires recently worked on or change wheels recently did you?
Contrary to popular belief, my 2012 4 Runner does not have the tire pressure sensing unit in the spare. The Toyota dealer advised me to pump up the 4 tires to 36 PSIG which I did. The light stayed off. Thanks for all your input.