What type of mouse, PS/2, USB, wireless?

Further tests to try;

1] PS/2 mouse. Try a USB mouse.

2] USB mouse, try a different USB port, and/or try a different USB mouse. Usually no software setup required.

3] Wireless mouse, check the batteries, (strange things can happen when they are low), make sure the receiver is not obstructed. If you have a wireless landline phone handset nearby, try moving that away. I understand some frequencies can clash.

See if any of that helps.