No, you don't. The "anti-virus" business model was a consequence on Windows' traditional vulnerability to viruses. Even Microsoft Windows is not as vulnerable to viruses as it once was. The multi-billion dollar "anti-virus" business is becoming just as irrelevant, a fact Symantec's own information security officer admitted some time ago. You can expect them and their sycophantic defenders to become increasingly shrill as it suffers its inevitable death throes. Some continue to do so even on this site.
To learn how to protect your Mac please read Effective defenses against malware and other threats.
Adware has emerged as an increasing threat to your Internet activity, but compared to true computer viruses (of which there are exactly none for OS X) adware is a mere inconvenience. Besides, you have to devote some effort into installing adware. To learn how to recognize adware so that you can avoid being deceived into installing it, please read How to install adware. Even if you were to do so in spite of all the roadblocks OS X presents in an effort to warn you about its consequences, it's easily removed.
Beware bogus Adobe Flash "installers" also.