I'm assuming you don't see it on the pictures (or on live-view, if your camera has it). Look inside the body at the mirror, as had been previously noted, but also look at the bottom of the pentaprisim (will be directly above the mirror), as the dust may be there; as that gets magnified, it will look larger. Be very careful cleaning there, as that could affect the veiwfinder's information screen.
If it is in both viewfinder and live-view/shot, it is going to be the lens.
Tue 26-Mar-13 07:24 PM | edited Wed 27-Mar-13 01:28 AM by GodFather2u
I had the same problem, then started getting dust on the sensors. I was able to clean the dust from the sensors, but the viewfinder debris wouldn't go away. I started developing this debris/dust after 1500+ shutter clicks. The debris from the viewfinder never showed up in any photos, but the dust was visible (barely).
I sent it to Nikon and they cleaned it up under warranty. BUT THAT'S NOT ALL!! They replaced the Shutter Mechanism as well. I don't know if this is the solution to the dust problem everyone else seems to be having.
I'll update after another 1000+ shots unless someone else post something regarding the Shutter Mechanism replacement as a "cure" to the dust problem.