It would really be beneficial to you if you were alot more specific. What kind of pop ups? What operating system are you running? etc etc.
Even without that information, I can tell you that it's probably just some form of spyware. Download and install Ad-Aware 6 from <A HREF="http://www.lavasoft.com" target="_new">LavaSoft</A> and let it do it's scan, then delete all of the items it lists when the scan is complete.