  We study the properties of entanglement entropy among scattering particles as
observed from different inertial moving frames, based on an exemplary QED
process $e^+e^-\rightarrow\mu^+\mu^-$. By the explicit calculation of the
Wigner rotation, the entanglement entropy of scattering particles is found to
be Lorentz invariant. We also study the behavior of the entanglement between
spin degrees of freedom for scattering particles in moving frames. This
quantity, being found to change with different inertial reference frames, does
not exhibit as a Lorentz invariant.
