Sensorimotor rhythm-based brain-computer interfaces (SMR-BCI) may enable patients with prolonged disorders of consciousness (PDoC) or severe physical impairment to learn to intentionally modulate motor cortical neural oscillations. SMR-BCI could mitigate the need for movement-dependent behavioural responses, hence providing diagnostic information and/or communication strategies. Here, an SMR-BCI was evaluated in a three-staged protocol for PDoC. Stage I assessed awareness and capacity to modulate brain activity intentionally. Stage II facilitated SMR-BCI learning via stereo-auditory feedback training. Stage III tested use of SMR-BCI to answer closed categorized yes/no questions. Out of 14 patients with PDoC and locked in syndrome (LIS), eight patients showed capacity to modulate brain activity during stage I and thus participated in stage II. For practical reasons only five of these patients completed stage III. Two able-bodied participants were enrolled for benchmarking. Five of the eight participants performed significantly greater than chance level in 50-100% of runs (p< 0.05). Average top run performance accuracy correlated with diagnoses category. Participants across the PDoC spectrum showed capacity to engage with SMR-BCI to answer closed questions.