Recent advances in deep learning have made a progressive impact on BCI researches. In particular, convolutional neural networks (CNNs) with different architectural forms have been studied for spatio-Temporal or spatio-spectral feature representation learning. However, there still remain many challenges and limitations due to the necessity of a large annotated training samples for robustness. In this paper, we propose a semi-supervised deep adversarial learning framework that effectively utilizes generated artificial samples along with labeled and unlabelled real samples in discovering class-discriminative features to boost robustness of a classifier, thus to enhance BCI performance. It is also noteworthy that the proposed framework allows to exploit unlabelled real samples to better uncover the underlying patterns inherent in a user's EEG signals. In order to justify the validity of the proposed framework, we conducted exhaustive experiments with 'Recurrent Spatio-Temporal Neural Network' CNN architectures over the public BCI Competition IV-IIa dataset. From our experiments, we could observe statistically significant improvements on performance, compared to the competing methods with the conventional framework. We have also visualized learned convolutional weights in terms of activation pattern maps, separability of extracted features, and validity of generated artificial samples.