Are you running in borderless window or fullscreen? I'd recommend fullscreen, it might fix it.

save then quit game
go to screen saver setting
disable
game away!

Fullscreen Yes !! So clever!.
And I after playing. I go back to screen saver setting, and put on...
And to play, I go to screen saver setting and put off.. And after, I go back to screen saver stting and put on...
You're the man, thank you for your help...

And you never thought of this yourself? Wow!

Thanks for your comment. Another clever guy, I am lucky...

Well it's like...
davidtt: I get wet if I go into the garden with the lawn sprinkler on.
kyussmanchu: Then turn the sprinkler off first.
davidtt: Yes, you're the man... so clever. Thanks for the help.

I wasn't being sarcastic...How the hell do I know that you're not some PC newby? Maybe next time try posting what solutions you tried before getting all pissy when people give you basic solutions.
Also, if the issue is that the screen saver keeps launching during gameplay, should that not be an OS related issue? Not sure what the game has to do with that to be honest.

Most games disable the screensaver but for some reason The Witcher 3 doesn't. I don't think this is a solution being sought, but simply a complaint. Maybe it might be fixed in a future update if enough people complain.

Not quite. It is not a game's responsibility to disable screen savers. It is a game's responsibility to tell the operating system (Windows) that it is active, so that Windows can manage things like screen savers appropriately. In the case of the OP, it appears that he/she has set the screen saver to kick in far too quickly, noted by the need to wiggle the mouse etc. during cut scenes. It should be a simple matter to set the screen saver to only kick in after, say a half hour of input inactivity. Problem solved.

Thanks for understanding it. That's the point. Like all the games, it will be a nice feature.
I hope they will integrated it in a future update.