Buildings can be viewed as small cities due to their size, users, and mixed complex activities. Similar to that in smart grid, Demand Side Management (DSM) in micro grid plays an important role in achieving effective and reliable energy management in buildings. In this paper, in order to reduce the Peak-to-Average Ratio of energy consumption and guarantee fairness between users, we investigate fair load scheduling for DSM based on Narrowband IoT (NB-IoT) technology in smart building. Firstly, the load scheduling model based on NB-IoT is constructed. Then, considering the constraints of energy consumption, energy storage and energy generation in buildings, a minimum-maximum fair energy load scheduling problem with PAR limit is formulated into Linear Programming (LP) and solved by commercial software CPLEX. Finally, simulation results validate our proposed optimization method to achieve fair load scheduling with DSM mechanism by comparing with the case without DSM mechanism in smart building.