The validity of a hybrid of Brownian dynamics and lattice Boltzmann methods for simulating the activation of Brownian motion of magnetic particles in suspension was examined. In this method, random forces were added to the equations of motion of magnetic particles in the usual Brownian dynamics. In order to activate the Brownian motion at a physically reasonable level, a viscosity-modifying method was introduced in adjusting the random displacements of the particles. The main results obtained are summarized as follows. The aggregate structures of magnetic particles were in good agreement with the results of the Monte Carlo method, and the pair correlation functions agreed well with the Monte Carlo results both qualitatively and quantitatively: the Monte Carlo method is a well-established method and is regarded as yielding theoretical solutions. The e magnetization curves were also in good agreement with Monte Carlo results, and this verifies that the rotational Brownian motion is activated at a physically reasonable level. The viscosity-modifying coefficients were almost independent of the strengths of the magnetic particle-particle and the particle-field interactions, and also of the volumetric fraction. From these results, we conclude that the present hybrid simulation method has potential for investigating the behavior of magnetic particles in a non-uniform applied magnetic field and in a general flow field.