Mobile health (mHealth) technologies play a fundamental role in epidemiological situations such as the ongoing outbreak of COVID-19 because they allow citizen to self-monitor their health status while staying at home and being constantly in remote connection with the physicians despite the quarantine. Special care should be given to self-monitoring vital parameters such as blood oxygen saturation (SpO2), whose abnormal values are a warning sign for potential infection by COVID-19. Measurement of SpO2 is commonly made through the pulse oximeter that requires skin contact and hence could be a potential way of spreading contagious infections. For this reason, contact-less solutions for self-monitoring of SpO2 would be beneficial. In this paper we present a mHealth approach to self-monitor SpO2 that does not require any contact device since it is based on video processing. Video frames of the patient's face acquired by a camera are processed in real-time in order to extract the remote photoplethysmography signal useful to derive an estimation of SpO2. Preliminary experimental results show that the SpO2 values obtained by our contact-less solution are consistent with the measurements of a commercial pulse oximeter used as reference device.