A numerical investigation is carried out to assess the effect of magnetic field on the entropy generation characteristics of a magnetic nanofluid flowing between parallel plates using the two-phase mixture model. The magnetic field is generated by one or multiple line dipole(s). The influences of Reynolds number, magnetic field strength, number of dipoles and also their arrangement are examined on the thermal, frictional and total entropy generation rates both locally and globally. The application of a magnetic field leads to rotation of magnetic nanofluid and consequently, mixing in the flow and more uniform temperature distribution. The results show that augmenting the magnetic field strength from 0.01 Am to 0.1 Am, at Reynolds number of 500, results in a 2.93% increase and a 5.54% decrease in the global frictional and thermal entropy generation rates, respectively. Moreover, it is reported that increasing the Reynolds number from 500 to 2000, for a magnetic field with strength of 0.1 Am, causes an increase of 63.02% and a decrease of 50.45% in the global frictional and thermal entropy generation rates, respectively. In the case of one dipole, the results reveal that the position of the dipole has no effect on the global total entropy generation rate, but this is not true for two and three dipoles cases. (C) 2018 Elsevier B.V. All rights reserved.