This paper analyzes the involvement of the cerebral area during robotic assisted gait training on a treadmill (Lokomat) in the two cases of passive and active locomotion. Imaging of the brain activity in such a natural environment is allowed by Mobile Brain/Body Imaging (MoBI) approach with high-density electroencephalography (EEG), which we used to characterize the differences between conditions. A key feature for this research is the pre-processing of the brain signals, which are recorded in a noisy and artefactual environment. For this reason, we analyzed the efficiency of Artifact Subspace Reconstruction (ASR) as cleaning method. We employed EEG, electromyography (EMG) and force-measuring treadmill to record brain and body signals from 5 healthy subjects walking with Lokomat.