The camera follows selected ships. It does not follow unselected ships. I just click on empty space to deselect everything, and the camera stops moving. You can use fleets to reselect ships, or just do what I do and put a big dragging box over everything when you want to reselect them.
It certainly
does follow unselected ships. I do that all the time.
Also, hitting ESC, as previously suggested, does nothing.
What game are you guys playing, anyway?