  We have conducted VLBA phase-referencing monitoring of H2O masers around the
red supergiant, S Persei, for six years. We have fitted maser motions to a
simple expanding-shell model with a common annual parallax and stellar proper
motion, and obtained the annual parallax as 0.413+/-0.017 mas, and the stellar
proper motion as (-0.49+/-0.23 mas/yr, -1.19+/-0.20 mas/yr) in right ascension
and declination, respectively. The obtained annual parallax corresponds to the
trigonometric distance of 2.42+0.11-0.09 kpc. Assuming the Galactocentric
distance of the Sun of 8.5 kpc, the circular rotational velocity of the LSR at
the distance of the Sun of 220 km/s, and a flat Galactic rotation curve, S
Persei is suggested to have a non-circular motion deviating from the Galactic
circular rotation for 15 km/s, which is mainly dominated by the anti rotation
direction component of 12.9+/-2.9 km/s. This red supergiant is thought to
belong to the OB association, Per OB1, so that this non-circular motion is
representative of a motion of the OB association in the Milky Way. This
non-circular motion is somewhat larger than that explained by the standard
density-wave theory for a spiral galaxy, and is attributed to either a cluster
shuffling of the OB association, or to non-linear interactions between
non-stationary spiral arms and multi-phase interstellar media. The latter comes
from a new view of a spiral arm formation in the Milky Way suggested by recent
large N-body/smoothed particle hydrodynamics numerical simulations.
