malware virus from clicking on a cat video on facebook. Is this possible or just a scam?

iMac Maverick 10.9.5 I clicked on a cat video on facebook that had not been posted by any of my contacts; immediately a screen appeared with a warning that my computer may have been infected with malware and not to do any online banking and phone the 1 866 etc #. I did not get any further details just closed it immediately. Was this a scam to make me call the number or do I now have the virus? Has anyone else encountered this?