My mom always froze nuts to keep them fresh, so I do the same.  I have pecans and walnuts in ziploc bags in the freezer right now.

On a side note, she'd make this amazing pound cake that had black walnuts and maraschino cherries in it.  What I wouldn't give for some black walnuts right now to make some of those around Christmas to give as gifts.  Can't find 'em in a store near me.  You should sell them!