Sorry I didn't mention earlier. I am using Unity plugin of EasyAR. In EasyAR SDK version 1.0 inside Engine class there is a function to obtain pojection matrix.
static Matrix4x4 GetProjection(CameraCalibration calib, float nearPlane, float farPlane)
But its not inside EasyAR SDK version 2.0. How to get it in updated versions of EasyAR.