Rust on pole pieces are very common, practically all should oxidise with time. should not affect your sound unless it's badly corroded, which also mean that they are very old already.
You can leave it as it is, but if you want to maintain it somewhat. Here is a tip.
Remove the strings.
Dab some Brasso onto a cloth, but NOT enough to make the cloth feel wet.
Polish 'on' the pole pieces with the brasso on the cloth.
Clean it up by polish 'off' the pole pieces with the clean dry part of the cloth.
Done, just clean the surrounding area too, where you can't reach with the strings on. Re-string your guitar and go.
You should be doing this at most half or once a year.
DO NOT use WD40, if you don't want a gooey feeling guitar.