In this paper, we present a brain-computer interface driven Motorized Ankle-Foot Orthosis (BCI-MAFO), intended for stroke rehabilitation, and we demonstrate its efficacy in inducing cortical neuroplasticity in healthy subjects with a short intervention procedure (~15 min). This system detects imaginary dorsiflexion movements within a short latency from scalp EEG through the analysis of movement-related cortical potentials (MRCP). A manifold-based method, called locality preserving projection, detected the motor imagery online with a true positive rate of 73.0±10.3%. Each detection triggered the MAFO to elicit a passive dorsiflexion. In 9 healthy subjects, the size of the motor evoked potential (MEP) elicited by transcranial magnetic stimulation increased significantly immediately following and 30 min after the cessation of this BCI-MAFO intervention for ~15 min (p=0.009 and p<0.001, respectively), indicating neural plasticity. In four subjects, the size of the short latency stretch reflex component did not change following the intervention, suggesting that the site of the induced plasticity was cortical. All but one subject also performed two control conditions where they either imagined only or where the MAFO was randomly triggered. Both of these control conditions resulted in no significant changes in MEP size (p=0.38 and p=0.15). The proposed system provides a fast and effective approach for inducing cortical plasticity through BCI, and has potential in motor function rehabilitation following stroke.