The nucleon effective mass, binding energy and neutron star configuration in the Relativistic Mean-Field Theory (RMF) is considered. The calculation are motivated by the construction of the equation of state for a neutron star in the RMF. The equation of state for the parameters set TM1 is calculated using the Feynman - Bogolubov variational method for temperature different from zero. The structure of the neutron star is presented. The maximal stable configuration are obtained for: M_max=1.91 M_Sun and R=12.84 km.