As long as there is no mucous, he is probably fine, but you need to find out the source if it is environmentally caused. One of our TLA fans found out that the scents she was using in her house was causing her budgie to sneeze. Maybe he's allergic to dust. Just take a look around your house and make sure your budgie isn't responding to an environmental factor. Also, if he takes baths and gets water up his nose, he might be sneezing that out as well.
Birds sneeze occasionally to clear their airways from dust and water so that would be normal unless you see discharge or if they are breathing with their beaks open. How is his eating and drinking? Is he behaving normally otherwise or is he less active, fluffed up and shaking at all?
From what you are describing it sounds pretty normal. Watch if he starts sneezing a lot and if there is any discharge or labored breathing or if he stops being his normal active self and please keep us updated.