help circle visible in viewfinder nikon D5100

I bought a new Nikon D5100, and have a minor query about the viewfinder. When looking through the viewfinder, I can see a very faint clear circle at the centre of the view (around the central AF square). It is around four times the width of the central AF square.it is small, It is more visible against a light background, and does not affect the picture (its not in the sensor, no dust). I have taken the lens off, and looked through the viewfinder without the lens and I can still see this circle (on what I assume is the focusing screen?).Is it normal? the circle is in the center, without the fresnel pattern of the screen that i see with the lens off and looked through viewfinder

Help please...