We have investigated the dynamics of a Josphson junction circuit, which consists of a dc biased Josephson junction coupled to a resonant tank. Numerical simulations indicate that period-3 and chaotic states coexist when this system is driven by a proper external dc current. The detailed structures of the attractors and the basins of attraction are given to specify the features of these states. This provides one with valuable information to avoid chaos in Josephson junction devices.