How can I get rid of a Macsecurityalerts.com on my Safari

Went to a website AccessBk.org. A small box appeared on screen that read " http://www.macsecurityalerts.com

VIRUS FOUND.

The last website you visited has infected your Mac with a virus. Press OK to begin the repair process. " I did not press OK. I forced quit, and then did restart, opened Safari, and the message is still appearing. Thanks for any help. My Mac is running OS X Yosemite : Version 10.10.2