  In the present work we use the mean field approximation to investigate quark
matter described by the su(3) Nambu-Jona-Lasinio model subject to a strong
magnetic field. We consider two cases: pure quark matter and quark matter in
beta-equilibrium possibly present in magnetars. The results are compared with
the ones obtained with the su(2) version of the model. The energy per baryon of
magnetized quark matter becomes more bound than nuclear matter made of iron
nuclei, for B around 2x10^(19)G. When the su(3) NJL model is applied to stellar
matter, the maximum mass configurations are always above 1.45 solar masses and
may be as high as 1.86 solar masses for a central magnetic field of 5x10^(18)G.
These numbers are within the masses of observed neutron stars.
