Game theory is an essential aspect of business and almost all the major B-schools have game theory as part of their curriculum. Whether it's a mandatory course or not might vary depending upon your institute.
I am sure you have all heard about the prisoner’s dilemma which was only the tip of a giant game theory subject. MBA is supposed to teach you how to make decisions that serve you in the best interest despite adversity and game theory could help you optimize your decision-making. All things said it’s not an easy subject.