I was searching in many forums regarding this issue like here and here, but they were mentioning using port 9390. I launched OpenVAS on port 9390, but I still get the same error.
I am using openVAS in msfconsole on Kali Linux. I load openVAS successfully, but when I try to connect, it shows me this error. 
  openvas_connect root toor 127.0.0.1 9390
    [*] Connecting to OpenVAS instance at 127.0.0.1:9390 with username root...
    [-] Error while running command openvas_connect: uninitialized constant OpenVASOMP::OMPConnectionError
    Call stack:
    /usr/share/metasploit-framework/plugins/openvas.rb:195:in `rescue in cmd_openvas_connect'
    /usr/share/metasploit-framework/plugins/openvas.rb:189:in `cmd_openvas_connect'
    /usr/share/metasploit-framework/lib/rex/ui/text/dispatcher_shell.rb:501:in `run_command'
    /usr/share/metasploit-framework/lib/rex/ui/text/dispatcher_shell.rb:453:in `block in run_single'
    /usr/share/metasploit-framework/lib/rex/ui/text/dispatcher_shell.rb:447:in `each'
    /usr/share/metasploit-framework/lib/rex/ui/text/dispatcher_shell.rb:447:in `run_single'
    /usr/share/metasploit-framework/lib/rex/ui/text/shell.rb:151:in `run'
    /usr/share/metasploit-framework/lib/metasploit/framework/command/console.rb:48:in `start'
    /usr/share/metasploit-framework/lib/metasploit/framework/command/base.rb:82:in `start'
    /usr/bin/msfconsole:49:in `<main>'
 
    