Absolutely! Even the darkest of Shakespeare's plays are full of comic relief in the form of humor, puns and goofy characters. Every drama needs comedy to lighten the mood and make the dramatic tension more meaningful so the full effect of the dramatic parts is felt.
Shakespeare often adds some comedy to his plays. Hamlet, Macbeth, Romeo and Juliet, to name a few, all have comedy interjected. It is generally known as "comic relief" because the tragedy is so overwhelming: murders, ghosts, etc. I like to think of it as the seventh inning stretch of tragedies. It gives everyone a little break, and for the Elizabethan audience, many of the jokes would have entertained them in the context of a modern environment (at least at that time). It gives everyone some breathing room before the intensity of the next sessions.
When looking at the use of humor in Shakespeare, do not overlook the actions and interactions of Samson and Gregory in Romeo and Juliet. "Do you bite your thumb at me sir...I do not bite my thumb but I do bite my thumb." And then his aside that essential says "Will I get in trouble with the Prince if I bite my thumb?"
Sometimes the work gets so serious and intense that the audience needs a little break. This is the "comic relief" referred to in post #1. The gravediggers in Hamlet are a good example, and in Macbeth there is an old gatekeeper who serves much the same purpose. Even a more historical and therefore more tragic (though non-Shakespearean) play such as Arthur Miller's The Crucible has some vestige of comedy, in this case through the often humorous remarks of Giles Corey.
Sometimes the comedy serves to heighten the attention in the serious themes of the work. In Hamlet, Hamlet has been talking about death throughout the play -- he own, his father's, Polonius's etc. But one of the funniest scenes is his tragic/comic conversation with the gravediggers. Scattered amongst the puns and the one-liners is a very serious conversation about what happens after death and how death is the great "equalizer" of all mankind. This funny conversation actually frees Hamlet to take the action he has wanted to take for nearly the whole play.
Are you just asking us to discuss this, or what? It is not too strange that Shakespeare put comedy into his tragedies. This is known as comic relief--the use of comedy to relieve tension in a serious work.
If this is not what you are asking, please clarify.
It is true that Shakspeare adds comedy with tragedy. While we are talking about Romeo and Juliet and Hamlet, we should not forget less popular plays as "Much Ado About Nothing" and "The Midsummer Night's Dream". Based on a rather comic scenario, they gave an impression of being comic play. Then name itself reflects (Much Ado About Nothing) a comic sense. Shakespeare combines comedy, tragedy, romance and human nature in his plays which not only draws attention of many literature readers but also, make them more interesting to read.