Variability of the Radio Nucleus of the Galaxy M81

M81 is the nearest galaxy with an active galactic nucleus, with the possibly exception of Cen A. The nucleus is exceptionally compact. Here we present results from new VLA and VLBI observations of the nucleus of M81. The VLA shows that its flux density and spectral index are variable by 50% on a timescale of weeks. The VLBI imaging results show that there is structure on scales <0.5 mas, and that this structure is variable, also on a timescale of weeks.