ur6beersaway :
Not recommended.http://www.bleepingcomputer.com/forums/t/186533/is-it-bad-to-run-multiple-antivirus-programs/
Having more than one antvirus is only a problem when they provide real-time scanning. Real-time scanning is when they actively monitor your files. Everything you download gets scanned, everything you open gets scanned - it just monitors your system in general, even when the computer is idle.
Norton & AVG both provide real-time scanning, hence it was not recommended in your linked thread.
While Avast! is a real-time scanner, Malwarebytes free is on-demand. This means it only scans when you open it and press scan (or have it set on a schedule). The rest of the time it does absolutely nothing, so is fine to run alongside Avast!. And Comodo is almost unrelated as it's a firewall and not AV.
In summary - You can have as many antivirus/malware programs as you like, but only one should be performing real-time scanning/active file monitoring/email scanning etc. Everything else should be on-demand scanners.