As others have mentioned, that seems normal, though you may have more dust at home than others. Nothing to worry about, you can wipe it off.

My personal recommendation would be to wipe it off when the fans are off. Otherwise you risk of loosening up the dust and just get it sucked into the computer, defeating the purpose of wiping it off. You can use a slightly damp wipe (make sure there is nothing dripping or you may cause problems) or electrostatic brush to capture most of it, but even a dry wipe will do the trick.