If it's not the "natural", freshly ground, no preservatives kind, it will last a very long time. I don't even keep mine in the fridge (who can spread it when it's cold!
). I think the longest I've had any around is a little over a year and it's still been fine as long as the lid is kept tight.
If it's "Natural" PB, then I think it will probably go rancid faster, but certainly not after 3 months in the fridge