Active USB port on shutdown

I have an Acer laptop. When I shut it down i.e switch off, the usb port I use for my mouse (I don't use the touchpad) sometimes stays active. By that I mean, the little light on the mouse stays illuminated evn when the computer is switched off and is not plugged in to a power source. This happens only sometimes. The fact that is happens on an irregular basis seems strange. I would have thoiught that the USB port was either on full time or off fulltime when the computer is switched off. Whereas this is not a real problem, it is rather strange that it happens intermittently. Anyone care to comment. Many thanks, Brian

i think most laptops have an active usb on shut down you can turn iit off in your makers setting