When you look at a mirror, you are looking into the mirror
Your focal length in a mirror is your distance away from the mirror, plus the distance of the object away from the mirror. When you look at an object in a mirror, you are seeing a virtual image the exact distance it is away from the mirror. So, if you are standing 1 foot away from a mirror, and focus on your face, you are actually focusing at 2 feet.
To try this out, put a piece of tape on a mirror, about eye level. Standing in front of the mirror, focus your eyes on the tape, now your face is out of focus. Focus now on your face, and the tape is out of focus.