In this paper, we suggest a framework for power saving (PS) MAC protocol in a one hop mobile ad hoc network with a coordinator, and propose affinity based scheduling algorithm. Affinity is a novel concept that we introduce first. We define two types of affinities, i.e., node affinity and task affinity. Node affinity is defined as the weighted sum of incoming and outgoing task flows at each node, and task affinity as the sum of node affinities of source and destination nodes of each task. Our proposed scheduling algorithm has the advantage of putting more nodes into doze state for energy saving after completion of each task. To maximize the PS effect, we combine shortest job first scheduling with affinity based scheduling. We also devise an enhanced 802.11 PS MAC protocol by applying our framework and scheduling algorithm to the 802.11 MAC protocol which prevails in real world. Simulation results demonstrate that our scheduling algorithm and PS MAC protocol improve power efficiency and throughput significantly over other competitive schemes.