During an extended energetic particle event upstream of the earth's bow shock on September 5, 1984, a brief burst of energetic O+ ions have been observed using the time-of-flight spectrometer SULEICA on the AMPTE/IRM spacecraft. The event occurred during very active geomagnetic conditions. The onset of the O+ event coincides with a brief electron burst. O+ is predominantly streaming into the sunward direction, while the H+ and He2+ ions exhibit a net flow toward the bow shock with a second order anisotropy perpendicular to the interplanetary magnetic field (which was almost radial throughout the whole event). The energy spectrum of O+ is significantly harder than those of H+, He2+ and CNO (Q>2). The observations of two particle populations, different in temporal evolution, anisotropies and energy spectra, are discussed in terms of bow shock accelerated ions over the entire time period accompanied by a brief injection of magnetospheric particles.