Interference limits the throughput of a mobile ad hoc network (MANET). Multi-antennas can be employed at a node for interference cancellation besides attaining array gain. Spatial interference cancellation requires each node to estimate the interference channels, which is potentially inaccurate due to node mobility. As a result, maximizing the network capacity requires optimally allocating spatial degrees of freedom (DoF) to cancel interference and enhance link reliability based on the node mobility. This paper addresses this issue for a MANET with Poisson distributed transmitters and employing zero-forcing beam for spatial interference cancellation. Specifically, the residual interference power for each node from partially canceled interferers is characterized as a function of Doppler frequency and the number of DoF for interference cancellation is shown to decrease with the Doppler frequency. The adaption of spatial interference cancellation to mobility is observed to significantly improve the network performance in terms of both outage probability and capacity compared with the case without adaptation.