Adblock Plus only gets rid of adverts which are embedded in pages. i.e. ads which were put there by the website which you're viewing, like the ones here on AB. They don't get rid of pop-ups.
If you're getting pop-ups then you've got malware on your computer. Download, install and run the free version of Malwarebytes Anti-Malware to get rid of it:
https://www.malwarebytes.org/
(NB: When installing it, take care to remove the tick alongside the pre-selected option to take a free trial of the Premium version).