  Through very long baseline interferometry observations of one of the closest
low-luminosity active galactic nuclei M81* at multifrequencies of 8.8, 22 and
44GHz, a bright discrete knot with an unusual low apparent speed $\sim$0.1c was
detected. Combining with the contemporary monitoring of X-rays data at 2-10keV,
it indicates that a moderate X-ray flare happened when the knot launched from
the core region. Three possible origins of the knot are proposed to explain our
observational results. They are an episodic jet ejection, a low-speed shock
wave, and a possible secondary black hole in a binary system, respectively.
Future intensive multiwavelength monitoring can help to understand the discrete
knot as well as the central black hole better.
