Whether a rabbit sneezing is normal or not depends on a couple factors. If it's an occasional sneeze (<5 a day maybe with no other symptoms), then it likely is reaction to dust or something. When frequencies are higher, and especially paired with nasal discharge, wheezing sounds, or runny eyes, then it is more likely to be something like an upper respiratory infection. URIs and other ailment-related reasons for sneezing do require veterinary assessment to properly treat. You can see here for lists of rabbit vets: Choosing a rabbit veterinarian - WabbitWiki , and here for information on URIs specifically: Snuffles - WabbitWiki
Sometimes hay can be dusty. Or a piece of hay (or fur) can get in their nose and tickle it, causing them to sneeze. With sneezing, keep an eye out for any discharge that is not clear. Clear discharge isn't much to worry about (unless it is excessive).