Status bar > Time controls > Previous Frame
Keyboard > , (comma)
Previous Frame moves the time slider back one frame.
If Key Mode is on, the time slider moves to the previous keyframe. Keyframe options are set in the Key Steps group of the Time Configuration dialog. If Use TrackBar is turned on, Previous Frame jumps to the previous key of any kind. If Use TrackBar is turned off, Previous Frame will jump to the previous transform key, ignoring any other type of keys.