One of the challenges for implementing 60GHz based wireless networks is the large amount of power consumption due to the large number of antenna elements. Decreasing the beamwidth of each link, each link obtains higher spatial reuse gain, however, the energy consumption is increasing dramatically due to the increased number of antenna elements. In order to tradeoff the energy consumption and the spatial reuse gain obtained by directional antenna array, the antenna beamwidth has to be optimized. In this paper, the beamwidth optimization problem is formulated as an energy consumption minimization problem subject to a required data rate. Due to the randomness of topology, a probabilistic model is used to analyze the problem and to derive optimized beamwidth. Moreover, based on the analysis results, we propose an antenna muting scheme based on the distance of links to adjust the beamwidth of each link. According to our simulation results, the proposed scheme can save energy consumption up to 80% with an 8 × 8 antenna array.