An on-package dual-mode square-loop band pass filter is studied by applying a non-uniform finite difference time domain (NU-FDTD) method. The filter is integrated on a package containing a transceiver, and it is designed to operate in dual-modes, i.e., and , to ensure a good electric performance around the center frequency at 5.25 GHz, which is commonly allocated in wireless local area network (WLAN). This filter is also referred as a dual-mode integrated-circuit package filter (DM-ICPF) based on its operational mode and integration onto an IC-package. The frequency characteristics in terms of the scattering parameters are studied, and the results are validated against the computed results using commercial software, the high frequency structure simulator (HFSS). Results show an excellent agreement between the numerical data, and the proposed DM-ICPF structure can be applied in the area of the highly integrated wireless transceivers.