my phone may have virus but my antivirus scans clean that phon is protected
A lot of advertisers try to mislead you by saying there is a virus on  your phone. I believe Google banned the use of misleading advertisements such as the one you are speaking of.  So if it was a pop-up ad, I would not worry about anything. Just be aware that some pop-up ads on websites don't have a cancel button, and if you press the back button on your device, it's like you pressed OK.