The time-dependence of strain under constant magnetic field and set temperature was studied in Ni2MnGa ferromagnetic alloys. Structural aspects of dynamic response of martensite under constant magnetic field were investigated with X-ray diffraction and magnetisation measurements. It was found from comparison of the time dependence of the magnetic field induced strain with that under constant applied external stress that the material gradually deforms under constant magnetic field at set temperature in a manner analogous to creep under a constant applied compressive stress.