In this paper, a passive bistatic radar system using television as opportunistic illuminator is presented. When considering the existence of clutters, a new method is proposed to track a variable number of targets in a cluttered environment. A clustering algorithm is first introduced to judge whether a new target appears or an existing target vanishes, and then the UKF based cheap joint probabilistic data association method (UKFCJPDA) is used to track the targets. Numerical simulation shows good performance of this algorithm.