The previous study demonstrated that the radio frequency plasma-oxidized approach could successfully convert methane/oxygen mainly into syngas. However, the trace toxic polycyclic aromatic hydrocarbons (PAHs) were obtained and examined in this study. To convert pure CH4 produced the maximum amounts of PAHs, reaching 15.0 mu g/g of CH4 converted, at 90 W and 1.33 kPa. However, elevating the inlet O-2/CH4 molar ratio to 1.5, the minimum PAH emission rate was achieved, to be 2.46 mu g/g of CH4 converted at 90 W and 4 kPa. In addition, the emission characteristics of individual PAH mass, the PAH homologues, and the toxicity were also discussed. Moreover, the association of acetylene selectivity with PAH mass was fairly consistent, to reveal that the acetylene addition mechanisms might play an important role in the plasma conversion system.