Most browsers haver built-in pop-up blockers. Look through the 'Options' section to see whether it's enabled. (In Firefox it's under Tool > Options > Content).
However I suspect that your pop-ups are being generated by malware anyway (so your browser's pop-up blocker won't be able to deal with them). Download the free version of Malwarebyte's Anti-Malware:
http://www.malwarebytes.org/products/malwarebytes_free/
Install it, taking care to remove the tick when you're offered the opportunity to take a free trial of the 'PRO' version.
Run a scan with that program and remove anything dodgy that shows up. Your pop-ups will then (hopefully) disappear.
Chris