Depends on the shot. From patching up a still frame in Photoshop to masking and cloning in AE to simply covering things up with another photo or using effects this could be anything. Impossible to advise specifically without having seen at least a screenshot of your footage.
If your actor is moving in the frame then you may be able to use an earlier frame to replace the background. If the camera is moving this will involve some tracking. As Mylenium said, without seeing the shot it's impossible to point you to the most efficient and effective solution.
We haven't heard back from you. Still need help? Let us know.