The binding posts on the back of my amplifier are quite loose. They’re not causing a problem, mind you, because music still plays through fine. But is it dangerous?
I think it’s safe to assume that anything loose on a piece of audio component could be a hazard. So, definitely, tighten ‘em up. It should be a fairly easy job providing the posts aren't damaged or too worn. Depending on your level of technical proficiency, it might be something you can do yourself (please make sure the amplifier is unplugged if you try). Otherwise, find a technician.