Do you mean when you are browsing the Internet? I run Firefox and there is an add-on called Adblock Plus - I use that and I don't get any problems with pop-ups. You can also add it through Google Chrome.
I'm using IE as my brouser. In "tools" select, "pop up blocker". From here you can turn the pop up blocker on and off and you can alter the "blocking level" as well.
To stop pop up in internet explorer first of all open the browser then click on the Tools menu and choose the pop up blocker option. Then restart your IE browser.
To stop pop up in Mozilla Fire Fox first of all open the browser and click on tools. Then select the option from the menu and hit the content tab. Check the “block popup windows” and restart your browser.