  Long-term neutrino-radiation resistive-magnetohydrodynamics simulations in
full general relativity are performed for a system composed of a massive
neutron star and a torus formed as a remnant of binary neutron star mergers.
The simulation is performed in axial symmetry incorporating a mean-field dynamo
term for a hypothetical amplification of the magnetic-field strength. We first
calibrate the mean-field dynamo parameters by comparing the results for the
evolution of black hole-disk systems with viscous hydrodynamics results. We
then perform simulations for the system of a remnant massive neutron star and a
torus. As in the viscous hydrodynamics case, the mass ejection occurs primarily
from the torus surrounding the massive neutron star. The total ejecta mass and
electron fraction in the new simulation are similar to those in the viscous
hydrodynamics case. However, the velocity of the ejecta can be significantly
enhanced by magnetohydrodynamics effects caused by global magnetic fields.
