Having worked as a loader/2nd AC and getting thrown into the focus puller chair on some b-roll - focus is changing constantly. On a movie set, it’s pretty much an entire person’s job.
Unless the distance of the camera and the subject do not move at all, the focus will be actively changing - yes.
Depending on various conditions (lighting, lens choice, etc) there might be a very large distance range that is in focus - or it might just be a few inches. Even if the focus puller isn’t doing any big focus swings, they are likely making small adjustments.
