In this study, we analyzed brain connectivity profiles from mild traumatic brain injury (mTBI) patients and normal controls. We computed Granger causality measures from magnetoencephalographic (MEG) activity obtained at the resting state, in an attempt to understand how the default network is affected by mTBI. Our results show that all subjects exhibit a dense network of peripheral local connections. However, normal controls show an additional network of long-range connections that is drastically reduced mTBI patients. These findings suggest that analysis of functional connectivity patterns may provide a valuable method for early detection of mTBI.