As the world becomes more and more automated, the degree of cyber-physical systems involvement cannot be overestimated. A large part of them are safety-critical, thus, it is especially important to ensure their correctness before start of operation or reconfiguration. For this purpose the model checking approach should be used since it allows rigorously proving system correctness by checking all possible states. To ensure the compliance of controller-plant properties with system requirements, the closed-loop verification approach should be chosen, which requires not only a formal model of the controller, but also a formal model of the plant. In this paper we propose an approach for constructing formal models of context-free deterministic plants automatically using active learning algorithms. The case study shows its successful application to plant model generation for the elevator cyber-physical system.