ClamXav is a free malware scanner for Mac OS X. It uses the very popular ClamAV open source antivirus engine as a back end and has the ability to detect both Windows and Mac threats.

ClamXav for macOS can be setup up as passive or active: scan only the files you tell it to or your entire hard drive, whichever you prefer; you can also choose to activate Sentry to monitor your hard drive and scan new files as they arrive.

Features and Highlights

Easy to use
Clearly lists infected files. Save your favorite scan locations. Free virus definition updates.

Versatile
Exclude files or whole disks/folders. Quarantine or Trash files with one click. Schedule scans and updates.  

Powerful
Use the bundled ClamAV engine or bring your own installation. Monitor your disk with ClamXav Sentry.

Note: 30 days trial version.