Weird question. I think you may have the wrong play here, but I'm going to answer as if you've put this in the right spot.
The short answer is it's NOT a comedy.
Although Othello is certainly funny in spots and frequently ironic, it is not a comedy. It can't be. Comedys and tragedys may have similar plot complications, but a comedy invariably ends well. To qualify as a comedy, the protagonist (or some other central character) should experience a rise in fortune. In comedy, problems do not end in the death of characters we have become attached to; instead, issues are resolved, endings are happy and audiences go home smiling.
A tragedy, however, never ends well. It involves the downfall of a hero, a mostly good but flawed individual. The weakness or the flaw doesn't have to be a bad quality. It can be a virtue that the character has in excess, or it can be a vice. Invariably, this quality leads the character to make decisions that have terrible consequences. Bad things happen. People die, often innocents. The audience feels pity and fear (according to Aristotle). The protagonist may have a final insight or understanding. The audience leaves the theatre with smudged mascara and feels sad but "purged" as a result.
So...two reasons why this play can't be a comedy.
But as for the comedic elements...
1. the play uses a plethora of low humour: sexual references, insults, clever witticisms
2. the play is absolutely steeped in irony (practically every time "honest" Iago opens his mouth)