I was about to write a post about turbine stators, but barit 1 got in first with an excellent explanation. As barit's example shows, most of the torque in a turboprop is generated in the gearbox (and it is this that the torque gauge measures) but the turbine stator torque still contributes to the total.
We are all familiar with the idea that thrust is equal to the rate at which linear momentum is imparted to the air. By the same token, torque is equal to the rate at which angular momentum is imparted. As chornedsnorkack points out, the only way to eliminate torque is to elimnate the net angular momentum of the slipstream.