My pc shows a message that says 'detected virus activities' but my antivirus scan is norma

in the status bar of my main screen,there is a message that says 'critical system errors' and tells me to buy a virus protection software while I already have McAfee package, I also ran the windows spyware but its normal too,what can be the reason for this.

My pc shows a message that says 'detected virus activities' but my antivirus scan is normal, why?free spyware

Sounds very much like your computer is infected with the Zlob Trojan. Zlob Trojan generates 'Critical System Alert' and other fake warning messages, then tries to force you into buying rogue antispyware products. To remove these message and the trojan that generates them, download and scan your PC with SpyNoMore, it is the most accurate program in detecting zlob infections.

http://www.spynomore.com/trojan-zlob.htm

My pc shows a message that says 'detected virus activities' but my antivirus scan is normal, why?live update

That's just a pop-up trying to get you to buy some scamware.

Trust your _updated_ and properly executed virus scanner.

If you are really paranoid, go to one of the antivirus sites and use the online scan.
Probaly a false positive from McAffey to get you buy more of their products. They are famous for that.
because its malware google superantispyware and it will work for you
make scan by spybot or adaware se personal(free),do update for your anti virus too then scan.
it's not your pc that tells you you have virus, it's some trojan installed on your pc and trying to fool you. mcafee doesn't pick up this thing as mcafee is made to fight viruses, but not spyware. what you need now, is to get a good anti-spyware program to clean your computer.