1
Do you see a circle cursor with arrows inside it on the web page, if so, press your mouse wheel to disable automatic scrolling.
2
If that was not the problem, if you have a game controller connected to your PC, that is the usual cause of the automatic scrolling.
3
If that was not the problem, check the up arrow, down arrow, Home and End keys on your keyboard to see if one of them is stuck.
4
If that was not the problem.
Open Command Prompt, then paste in this command and press Enter:
msdt.exe -id KeyboardDiagnostic
Run that Keyboard Troubleshooter to see if that can solve the problem.
.
If that does not resolve this for you
Open Device Manager
Expand the Keyboards section
Right click your keyboard and choose 'Uninstall'
Then restart your PC