Why do I need anti-virus software?

You are required to have a virus scanner installed by the terms of use of the company you work for or are doing business with.
To scan files locally, over your network, or going outside your network. For example, via email.
Windows viruses may potentially run via Wine.
Discovered GNU/Linux malware are mitigated.

Open Source Antivirus

Avast Core Security. As per the vendor's website, this supports Ubuntu 16.04 and above.
GRAVITYZONE ENTERPRISE SECURITY. As per the vendor, supports Ubuntu 12.04 and above.
ESET NOD32 Antivirus Business Edition for Linux Desktop Vendor advertises Ubuntu support (other products for mail and file servers available).
F-PROT Antivirus for Linux Workstations - for home use. Please see XFProt.
Panda Cloud Cleaner Requires Facebook login.
Sophos Antivirus for Linux As per the vendor's website, 16.04 LTS and 18.04 LTS are supported.
Symantec Endpoint Protection Vendor advertises Ubuntu 14.04 and 16.04 support.

Programs are run as normal user, not root user
Open source - more eyes on the system source code
Diverse system configurations
Less malware actors overall focus on linux. However, proficient malware actors do target linux.