There's no need for antivirus on Android, but it simply offers some people a peace of mind that they have an extra layer of "protection" on their phone. Unfortunately this also often leads to a false sense of security as well.
So long as you're downloading reputable apps from Google Play, leaving the default security features turned on in the settings and not clicking on shady links or visiting bad websites, there's nothing that can infect or harm your phone. In many cases, an antivirus can't save you from these types of attacks, either, since they're things that you do — not something that randomly/accidentally happens without your knowledge.