The motion of relativistic test electron in a free electron laser can be altered significantly by an ideal coaxial wiggler field and uniform axial guide field. We have investigated group I, II and III orbits and finally have found that electron motion become chaotic at sufficiently high beam density and at sufficiently high amplitude of wiggler field. The threshold value of the wiggler amplitude for the onset of chaos is estimated analytically and confirmed by computer simulation. It is shown that the electron dynamic is nonintegrable. There is evidence for chaos from numerical calculation of Poincare maps and nonzero Lyapunov exponent using different approaches of Benettin's method which are described and compared. Moreover, it is shown that the particle motion become chaotic on a time scale comparable with the beam transit time through a few wiggler periods.