Having read about this in several guitar forums it usually has something to do with the pickguard itself. Some plastics as they age seem to attract static electricity. Frustrated tele players have used leather or wood pickguards to eliminate the problem but I would suspect just about any new pickguard would do the trick.
That said I would try two things before I bought a pickguard:
- Shield the entire backside of your pickguard and make sure the shielding touches the pot casing so it's connected to ground.
- Polish the guitar & pickguard once or twice with a good quality polish (I like Virtuoso) and see if that changes the surface sufficiently to reduce or eliminate the static.