An AlBN thin film with a boron content (B/(Al+B)) of 0.1 or 0.3 was obtained by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE) using EB-guns as group-III element sources and an RF radical source for nitrogen supply. We compared the characteristics of the film with those of AlN and BN films. By reflective high-energy electron diffraction (RHEED), we observed ring patterns in the AlBN film. The X-ray photoelectron spectroscopy (XPS) N1s peak of the AlBN film was observed at a binding energy between the peaks of AlN and BN. There was no evidence for phase separation in the film.