Window Focus Getting Lost Every Few Seconds?

Since past 2-3 weeks I have noticed an issue that bugs me too much. The focus on a window keeps getting lost automatically.

Lets say I am reading a page or writing in a textbox (like this one), the current focus would automatically get lost and again need to click somewhere in the program. I may be scrolling down using scroll bar of mouse or arrow keys of keyboard or my cursor is being pointed somewhere in a textbox. Because of this issue, I again have to click manually a program.

I tried googling but could not find a suitable solution or root cause of the issue. Maybe there is a program that gets activated automatically and focus shifts to that hidden program - however i could not find one.