Interpersonal synchrony is regarded as a key mechanism in social coordination and emotional co-regulation. In psychotherapy research, synchrony between therapist and patient has been shown to be associated with a stronger alliance and better treatment outcomes. However, psychotherapy frequently takes place in group settings in which patients engage and practice together, raising the question of whether synchrony also emerges between patients, under what conditions it occurs, and whether it relates to therapeutic progress. In this study, we investigate dyadic physiological synchrony in patients with depression participating in a mindfulness-based intervention. Using a hyperscanning approach, we simultaneously recorded electroencephalogram (EEG) and electrocardiogram (ECG) from two interacting patients. We present preliminary results and demonstrate the feasibility of this innovative hyperscanning setup, which allows for naturalistic patient-to-patient interaction during a structured therapeutic exercise. The study addresses a markedly under-explored field and provides new insights into how mindfulness-based dyadic interventions may contribute to treatment outcomes in group psychotherapy.