In this contribution, we discuss the statistical mechanical implications of the mean field Ehrenfest method of quantum/classical dynamics for a quantum harmonic oscillator in a classical heat bath using the Brownian motion Hamiltonian as a model. A mean field quantum/classical master equation is derived and compared to the corresponding Redfield master equation, and the deficiencies of the quantum/classical approach pointed out by analyzing the nature of energy/population relaxation and decoherence.