try not to touch/clean the mirror of an SLR camera - its a silvered mirror and very prone to scratches.
the most you can do is to use a blower to remove the dust. if you are unlucky enough to have water spots, saliva or other liquid fall on the mirror, you can try to use isopropyl alcohol on a cotton tip to remove it - but do it very gently and don't try to clean the whole mirror, just the affected part.
The mirror has a special coating on it. If the offending particle cannot be dislodged by air, I would send it for proper cleaning. You have to be careful with cotton coz it may leave cotton strands behind on the mirror after cleaning.
I think the original poster is using film SLR, not D-SLR. If film SLR, then there will be no C-Mos problem, but if D-SLR, then still better not to touch the mirror as to avoid more dust or scratches. D-SLR are expensive...better send to OEM to do servicing...