This study investigates the influence of treatment frequency (1-150 kHz) on the atmospheric plasma activation of both silicone and polyethylene terephthalate (PET) particles. These polymer particles with diameters in the range 3-5 mm, were treated using either helium or helium/oxygen gas mixtures, in a barrel atmospheric plasma system. The level of polymer particles activation was monitored using water contact angle measurements. The effect of plasma treatment frequency on barrel heating was monitored using an infrared thermographic camera, the maximum barrel temperature after 15 min treatment was found to be 98 degrees C at a frequency of 130 kHz. Optical emission spectroscopy was used as a diagnostic tool to monitor changes in atomic and molecular species spectral intensity with experimental conditions, as well as a change in electron energy distribution function. Electrical characterisation studies demonstrated an increase in plasma power with increasing frequency, in the range investigated. X-ray photoelectron spectroscopy analysis indicate an increase of oxygen content on polymer surfaces after plasma treatment. For silicone particles, the minimum polymer water contact angle was obtained by using a frequency of 130 kHz. After 15 min treatment time, the water contact angle decreased from 141 degrees to 11 degrees. While for PET particles the optimum treatment frequency was found to be 70 kHz, resulting in a water contact angle decreased from 94 degrees to 32 degrees. This lower frequency was used due to the partial melting of the PET (Tg of 80 degrees C), when treated at the higher frequency.