We have measured the magnetoresistance of metallic polyacetylene at temperatures T between 4.2 K and 0.3 K and in fields B up to 3.4 Tesla both parallel and perpendicular to the average current flow. We found an exclusively positive magnetoresistance scaling in low fields as B2/T2 for T < 1 K and as B2/T3 for T > 2 K. At high doping levels the magnetoresistance is small and saturates in high fields at low temperatures. These results are independent of the particular geometry used and will be discussed in terms of the magnetic field effect on the hopping conductivity.