High density electrocorticogram (ECoG) of motor cortex was recorded during awake surgeries of two subjects with respectively epilepsy and brain tumor. Subjects were asked to execute spontaneous hand movements: extension and flexion during the experiments. We investigated the ECoG in time frequency plane during these hand movements and computed event-related desynchronization (ERD) and event-related synchronization (ERS) levels of beta (8-32 Hz) and gamma frequency bands. The distribution of ERD and ERS over channels provided an idea about the spatial distribution of the cortical activity within each task. In both subjects, consistently, the scale of power changes in beta and gamma band was larger in hand flexion compared to hand extension. In addition, the spatial distribution of ERD in beta and ERS in gamma band during flexion was larger than extension but highly overlapped between these tasks. Gamma band was more spatially localized than beta band activity and cortical patterns were more distinct between the tasks. Our preliminary results indicate that the high density ECoG can be effectively used in awake surgery for functional mapping.