  In the last few years ARCADE 2, combined with older experiments, has detected
an additional radio background, measured as a temperature and ranging in
frequency from 22 MHz to 10 GHz, not accounted for by known radio sources and
the cosmic microwave background. One type of source which has not been
considered in the radio background is that of fast transients (those with event
times much less than the observing time). We present a simple estimate, and a
more detailed calculation, for the contribution of radio transients to the
diffuse background. As a timely example, we estimate the contribution from the
recently-discovered fast radio bursts (FRBs). Although their contribution is
likely 6 or 7 orders of magnitude too small (though there are large
uncertainties in FRB parameters) to account for the ARCADE~2 excess, our
development is general and so can be applied to any fast transient sources,
discovered or yet to be discovered. We estimate parameter values necessary for
transient sources to noticeably contribute to the radio background.
