We propose all optical virtual private network (VPN) using microwave photonic filter for the first time in orthogonal frequency-division multiple based passive optical network (OFDM-PON). In our scheme, optical resonator is used at optical line terminal (OLT) as a subsystem to design photonic bandpass filter (P-BPF). This filter has free spectral range (FSR) corresponding to resonator length. Using this property, VPN data modulated on passbands of P-BPF could be extracted among upstream data at OLT, and transmitted to optical network units (ONUs) without electrical processes. To overcome coherent interference problem in the resonator, spectrum broadening technique using clipping RF tone is applied. The proposed system enables dynamic bandwidth allocation between VPN and conventional upstream by adjusting tunable delay line in the resonator. Also it supports VPN communication regardless of optical wavelength.