My dog does not appear to have a cold but he keeps sneezing. Any ideas what has caused this?

Could be a lot of things. Is this something he has just started doing or has he always done it? (one of our dogs always sneezes if he's face to face with you, many sneeze when they lie on their backs). Have you started using something different around the house that could cause him to sneeze (hairspray, polish, cleaning materials etc)? Does he have any discharge from his nose? If you can't find any cause at home, it might be wise to take him to the vet to be checked out.

Sneezing can be caused by all sorts of things - primarily allergies, but also growths and tumours within the nose, dust, and even pet birds........  HE really needs to be seen by a vet to rule out some of the more life threatening reasons for sneezing.