Analytical expressions for the TE10 mode fields and the acceleration gradient for an electron are obtained in a plasma filled rectangular waveguide under the effect of an obliquely applied external magnetic field. The lower and upper cutoff frequencies for the mode propagation and the acceleration gradient for the electron are evaluated under the effect of various parameters. The acceleration gradient is increased with the microwave frequency and angle of magnetic field. It becomes reduced for the higher plasma density and stronger magnetic field. The larger acceleration of electron is achieved when $\omega_{\rm p}> \omega_{\rm c}$.