Certain antibiotics, particularly fluoroquinolones, induce the mutagenic SOS response and increase the levels of intracellular reactive oxygen species (ROS), which have been correlated with antibiotic lethality. Both SOS and ROS increase mutagenesis in treated bacteria, likely resulting in the appearance of resistant mutants during antibiotic treatments. However, the relative contribution of ROS and SOS on this antibiotic-mediated mutagenesis is currently unknown. We used the antioxidant molecule N-acetylcysteine (NAC) to study the contribution of ROS on the SOS response and mutagenesis mediated by the fluoroquinolone antibiotic ciprofloxacin (CIP). We show that NAC is able to reduce intracellular ROS levels, mitigating as well the SOS response caused by treatment with subinhibitory concentrations of CIP. This effect leads to the reduction of antibiotic-induced mutagenesis to levels comparable to a translesion DNA-polymerases (TLS) deficient strain, suggesting that ROS play a major role in SOS-induced mutagenesis. Collectively, our results shed light on the mechanisms underlying antibiotic-induced mutagenesis and pave the way for the use of NAC as a safe adjuvant in antibiotic therapy to inhibit antibiotic-induced mutagenesis, hence augmenting our capacity to fight against threatening bacterial infections.