Peanut butter will keep in the freezer for up to about 6 months before it begins to deteriorate in flavor.
If it is left for longer than 6 months, this does not necessarily mean that it will be unsafe to eat. However it may just develop a stale taste and not be as nice to eat.
If you place the frozen peanut butter into the refrigerator to thaw, this will help to sustain the peanut butter for longer than if you were to simply leave it out to thaw.