In this work, surface characterization and electrochemical measurement were employed to investigate the effects of magnetic field (MF) on the corrosion of Q235 carbon steel in a NaCl solution containing sulphate-reducing bacteria (SRB) or extracellular polymeric substances (EPS). Results demonstrated that a 150 mT MF enhanced steel corrosion in a SRB-containing NaCl solution by 202% calculated from weight loss with pitting corrosion as the main corrosion type. Either EPS or MF rendered steel corrosion, but a synergistic interaction between MF and EPS boosted up steel corrosion. This synergistic enhancement could be referred to the alteration in orientation of EPS induced by MF. The presence of higher percentage of chloride ions on the carbon steel surface manifested that MF initiated the erosion of chloride ions on the carbon steel coupon.