Accurate estimation of phasor is essential for wide area monitoring and control of power systems. The accuracy requirements of phasor estimation for various class of applications are outlined by the IEEE Std. C37.118. This paper presents a frequency domain interpolation approach for phasor estimation at off-nominal frequencies. The proposed approach involves quadratic interpolation of complex DFT coefficients corresponding to fundamental and two side bin's namely the DC and second harmonic components. The advantage of the proposed approach is that an explicit knowledge of frequency is not essential. The performance of the proposed approach is analyzed using standard test signals and simulated voltage/current signals of practical equivalent systems. © 2017 IEEE.