Particle of dust in my N90s

[Cande V Ananth]

Folks:

    I own an N90s, and I just noticed that there is a small black
    particle (perhaps dust) when I look through the view finder.
    Admittedly, this does not harm my pictures, but its bothering
    me. I looked on the mirror (didn't touch or attempt to clean
    the mirror), the lens, and the view finder, but am unable to
    locate the dust particle. 

    I'd appreciate any pointers as to how I can clean this particle.
    Thanks.

Cande Ananth