Do you mean tracking something and making that area blurred? It depends on the shot. Simple shots and simple blurs can be done in Premiere Pro, a more complicated shot would be better handled in AE unless you have something like the latest Borris FX suite.
We need more details unless you are experienced enough with tracking to figure it our on your own.
Well I was doing a video tutorial. And the screen recording get has some names that I need blurred out. The problem is that the tutorial guy does a few 'scroll up, scroll downs' so I need to be able to track the name during the scroll.