Enormous numbers of mobile health applications (mHealth apps) developed recently on mobile devices (e.g. smartphones, tablets, etc.) have enabled health status (e.g. sleep quality, heart rate, etc.) monitoring that is readily accessible to average mobile device users. Typically, such mHealth apps involve active usage of mobile device resources, such as on-board sensors, network bandwidth, etc. The rapid increase of these applications promotes the US FDA agency to put in place regulations on mHealth app risk assessment. But these existing and upcoming regulations have not yet been accompanied by a mobile auditing framework, which provides real-time monitoring of mHealth apps' resource usage and triggers alerts to users if abnormal resource usage patterns are detected. In this paper, we develop a low-overhead and non-obtrusive mobile auditing framework, called mAuditor, that specifically monitors in real-time onboard sensor and network bandwidth usage of mHealth apps. We carry out experiments using a diverse set of mHealth apps that are available on the Google Play App store. Our results indicate that mAuditor is able to detect the discrepancies between normal and abnormal resource usage patterns of mHealth apps.