Two formulations of the virial theorem are used in practice: one for separate particles and one for a continuous medium. The virial theorem for a system of charged particles which was given by Landau and Lifshitz in their book \emph{The Classical Theory of Fields} should incorporate both these formulations. However, there is an error there in the derivation of this theorem, which is based on transformation from a discussion in terms of particles to a discussion in terms of a continuous medium. Specifically, the selfeffect force of the charges is not eliminated. As a result, the infinite self-energy of the charges is not eliminated, and the corresponding final equation cannot be satisfied. In the present note, a refined formulation of the virial theorem for a system of charged particles is given. The renormalization of the total electromagnetic field energy is taken into account.