should nis run bkgrnd tsk whilst online video?

Hi I run win7 nis2011 all up to date.  Im just confused why while i was watching video (not entirely fullscreen, shrinks during ads) norton pops up and say performing background tasks!?  I was mousing too on and off.

I have optimize off too.

 

Thanks for input, my machine seems strong enough but it just has me wondering why is all.

 

Thanks :)