The spec is most likely located on the underside of the viewfinder screen, which is located above the mirror. DO NOT CLEAN, or even touch or brush the angled mirror inside your camera--the mirror is very fragile,very delicate,and its precise location is critical for autofocus accuracy. A mirror can be quite dusty and dirty and filmy,and not affect the viewing image very much. You can NOT, I repeat, can NOT see dust or lint or fibers on the mirror surface--that surface is not in focus; what you see is on the viewfinder screen, above the mirror.
Yeah, there could be a speck of lint (sweaters and knitted hats, gloves, etc, anything made of yarn are particularly bad for this, BTW) on the viewfinder screen. Remove the lens and then blow hard on your hand three or four times, to make sure no little spittle drops go flying, and then blow the lint or fiber off the viewfinder screen. Replace lens. Be happy!
Just as an aside--there are going to be more specks in the future. That is guaranteed. You might as well get used to it and not worry until there are many of them.