  Narrow-line Seyfert 1 (NLS1) galaxies are a peculiar subclass of active
galactic nuclei (AGN). Among them, TXS 1206+549 belongs to a small group of
radio-loud and gamma-ray-emitting NLS1 galaxies. We focus on the radio
properties of this galaxy by analysing archival, high-resolution, very long
baseline interferometry (VLBI) imaging observations taken at 8 GHz frequency in
six epochs between 1994 and 2018. Using the milliarcsecond-scale radio
structure, we can resolve a core and a jet component whose angular separation
increases by (0.055 +/- 0.006) mas/yr. This corresponds to an apparent
superluminal jet component motion of (3.5 +/- 0.4) c. From the core brightness
temperature and the jet component proper motion, we determine the
characteristic Doppler-boosting factor, the bulk Lorentz factor, and the jet
viewing angle. We find no compelling evidence for a very closely aligned
blazar-type jet. The parameters for TXS 1206+549 resemble those of radio-loud
quasar jets with a moderate Lorentz factor (Gamma~4) and theta~24 deg
inclination to the line of sight.
