  The asymptotic properties at future null infinity of the solutions of the
relativistic Vlasov-Maxwell system whose global existence for small data has
been established by the author in a previous work are investigated. These
solutions describe a collisionless plasma isolated from incoming radiation. It
is shown that a non-negative quantity associated to the plasma decreases as a
consequence of the dissipation of energy in form of outgoing radiation. This
quantity represents the analogue of the Bondi mass in general relativity.
