Why does a married man flirt with me at work?

A married man flirting may just be having fun, or he may enjoy being found attractive and get a boost to his self-esteem in the process. He may also be simply seeking to manipulate the relationship toward a non-sexual goal, such as conforming to a permissive work environment or securing a political ally.

Is it OK to flirt with married man?

Yes, people flirt, but married life is meant for flirting with ones spouse, not flirting elsewhere. Similar to the thrill of the chase, some married men flirt because its risky; they know its wrong and dangerous and could have dire consequences if they get caught. And thats where the excitement comes in.