This paper analyses the impact on the error vector magnitude (EVM) of the received carrier aggregated orthogonal frequency division multiplexing (OFDM) signal when it is passed through a nonlinear high power amplifier (HPA). This analysis will help to measure the quality of transceivers in modern communication systems, which are highly sensitive to nonlinear distortions caused by HPA. Specifically, the closed form expression of EVM is derived for dual band carrier aggregated OFDM signals with nonlinear HPA in the presence of multipath Rayleigh Fading channel. 2D generalized memory polynomial (GMP) model is used to characterize the nonlinearity caused by HPA. A good agreement between the simulation results and analytically obtained results is observed.