A few questions. You said "I've tried everything". What is "everything"? Is it an optical mouse or a trackball mouse? Is it wireless? You said "Seems to happen when I use the keyboard". Is it a combo unit where the keyboard and mouse came together? I doubt if it is malware causing this but you said you did a virus scan. Did you also to adware and spyware scans? Have you tried another mouse? Also, please follow the forum tip that was right above the box the you put your subject in.
Tip: If you are asking for help to troubleshoot a computer-related problem, please be sure to include all the necessary information (ie: operating system, model number, hardware, software, etc) that will help others identify your problem for a speedy resolution.