You could have tinnitus at a frequency you can't hear if the tinnitus arises downstream of auditory issues that reduce hearing sensitivity. For instance, if so

You could have tinnitus at a frequency you can't hear if the tinnitus arises downstream of auditory issues that reduce hearing sensitivity. For instance, if someone couldn't hear a certain frequency because the corresponding hair cells in their ears were damaged, they could still have tinnitus at that frequency arising from parts of the brain that process that frequency.