This error can happen with Linux or FreeBSD or whichever OS that ClamAV support.

When you run

clamscan

You get this error

LibClamAV Error: cli_loaddb(): No supported database files found in /var/db/clamav
ERROR: Can't open file or directory

----------- SCAN SUMMARY -----------
Known viruses: 0
Engine version: 0.95.1
Scanned directories: 0
Scanned files: 0
Infected files: 0
Data scanned: 0.00 MB
Data read: 0.00 MB (ratio 0.00:1)
Time: 0.001 sec (0 m 0 s)

It means that you have no database virus.

Just configure and run freshclam.

A sample freshclam.conf file:

DatabaseDirectory /var/lib/clamav
UpdateLogFile /var/log/freshclam.log
LogTime yes
LogSyslog yes
PidFile /var/run/clamd/freshclam.pid
DatabaseOwner clamav
DNSDatabaseInfo current.cvd.clamav.net
DatabaseMirror db.br.clamav.net
DatabaseMirror database.clamav.net
NotifyClamd /usr/local/etc/clamd.conf
SubmitDetectionStats /usr/local/etc/clamd.conf
DetectionStatsCountry BR