The What is Education?  blog for teachers states that having  a sense of humor is, 

 very useful in creating a classroom climate and the development of learning processes that are more healthy and enjoyable. In fact, Melissa Kelly said that a sense of humor is one of the keys to being a successful teacher. According to Melissa, teachers’ sense of humor can relieve tension in the air and can prevent the onset of disruptive student behavior in the classroom, and can be used as a way to attract the attention of students in the class. And most importantly, with its sense of humor, a teacher would show that he/she is a person who has a personality and mental health, to enjoy life, and be able to live a normal life without the stress of his/her career.

http://what-education.blogspot.ca/2013/06/the-importance-of-teachers-using-humor.html

I (Cathy) was delighted to see one of my student teachers, Carolyn,  using her sense of humor throughout her literacy lesson. Her grade one and two students found her quite amusing and would joke along with her.  Sometimes her humor was self-depricating, and sometimes it was as innocent as, “Who me?  I would never do that!”  It was never sarcastic and always made her students smile.  She even used it as a classroom management technique to keep the students focused and engaged.  When I asked her about  her technique, she said it made teaching and leaning more enjoyable.  Then she described an art lesson she had just taught using candle wax and water colours.  She drew a picture on the white paper using a white candle, so it was not visible.  While introducing the lesson she held up the paper and kept telling the students how proud she was of her picture.  When the students kept insisting there was nothing there, she applied the water colours and, of course, the picture magically appeared.  The humor came to play when she allowed each student to play the same joke on her as they created their pictures.  All of the magic pictures were displayed proudly in the hallway of the school.  Carolyn said the students still refer to it and giggle.

I think having a sense of humor is an asset.   We all definitely need to laugh more, especially in our schools.