  The excess radio background seen at $\simeq 0.1-10\,{\rm GHz}$ has stimulated
much scientific debate in the past years. Recently, it was pointed out that the
soft photon emission from accreting primordial black holes may be able to
explain this signal. We show that the expected ultraviolet photon emission from
these accreting black holes would ionize the universe completely at $z>6$ and
thus wash out the 21 cm absorption signature at $z\simeq$ 20 as well as be in
tension with existing cosmic microwave background anisotropy and average
spectral distortion limits. We discuss possible augmentations of the model;
however, it seems that an explanation of radio excess by accreting primordial
black holes is not well-justified.
