why does my mouse move on it's own?

Possibly:

Bad surface for the mouse. Get a mousemat or get a better mouse.

Shitty mouse. Get a better mouse.

Interference. Don't put your mobile phone next to your mouse cable!

I bet you are using it on glass, another reflective or glossy surface. Try it on different types of surfaces and it should work. Construction paper (not printing) , smooth carpet (really), but experiment til one works. People have a misconception that the mouse reflects, it doesn't.

Try cleaning your mouse. Keeping dust off of the sensor could fix this problem entirely.

Most likely its the surface ur using ur mouse on or the sensor at the bottem is dysfunctional.

try a new mousepad, if problem persists, the mouse is broken

its get faulty. Bring a new one. Moreover you can try to uninstall Mouse driver from device manager and reboot the computer.

virus or malware attacked on your computer. scan with a antivirus. or install new OS (windows or other)

i try that already