I would say no it's not a touch attack. A touch attack means that you only need to hit something on them (such as armor) and you don't have to penetrate that armor to affect them. With unarmed strike you are still trying to do damage to the person.
This could be wrong (I don't have my books in front of me) but this is how I would rule it.
If you are trying to deal damage, an Unarmed Strike is a normal attack, not a touch attack. If you're using your unarmed strike to trip or grapple, however, it's a touch attack, but that use doesn't deal damage- it simply is used as a lead-in for the following action.
Remember you CAN deliver a touch spell (like inflict light wounds) with an unarmed strike; but you have to roll a regular attack, and if you hit you do the damage PLUS the touch spell goes off.
If you're using your unarmed strike to trip or grapple, however, it's a touch attack, but that use doesn't deal damage- it simply is used as a lead-in for the following action.
Those are simply described as unarmed melee touch attack (for Trip) or melee touch attack (for grapple), not unarmed strikes.
And given that Weapon Focus: Unarmed Strike and Weapon Focus: Grapple are two separate feats, the implication is that you don't use an unarmed strike to initiate a grapple.