Hi rdavis,
It almost sounds like you may have Norton Online Backup program installed on your system - in addtion to the Comcast Norton Secrutity Suite's backup ability.
Please go to your Control Panel (Programs & Features in Vista, Win 7/8 or Add/Remove Programs in XP) and see if there is a Norton Online Backup listed. If you no longer use it, uninstall it. This should stop the popups.
While in the Control Panel, see if there is a listing for Norton 360 present - if there also uninstall it. Please note your Comcast version will be listed as Norton Security Suite and that program needs to stay. There may be addtional steps required - if your NSS starts to act up.
Let us know if this is what is happening.