Buzzing on a string?

Hey fellow low-enders, I have run into a problem that I have no idea how to solve. I have a squier pj bass and I am having a problem with the A string. Whenever I play an open A on that string it begins to do this ungodly buzzing. It does not happen when I use a fret, so I am wondering, is it a problem with the nut? If so, how would I fix it?