Deficits in postural stability in response to environmental challenges are seen in chronic low back pain (CLBP) patients with high fear of pain (HFP). Hence, it is essential to follow effective approaches to treat postural stability deficits and improve the health status of these patients. The current study aimed to compare the effects of cathodal and anodal transcranial direct current stimulation (c-tDCS and a-tDCS) over the left dorsolateral prefrontal cortex (DLPFC) on postural stability in non-specific CLBP patients with HFP. In this randomized clinical trial study, 75 patients were randomly assigned to left DLPFC a-tDCS, left DLPFC c-tDCS and sham stimulation groups (n = 25 in each group). All groups received a single-session 2 mA tDCS for 20 min, but the stimulation was slowly turned off after 30 s in the sham group. Before, immediately, 24 h and 1 week after the interventions, postural stability indices were assessed using a Biodex Balance System. A significant reduction in most indices was shown in both a-tDCS and c-tDCS groups after interventions (immediately, 24 h and 1 week follow-up) during static and dynamic postural tasks compared with the sham tDCS group (p < .01). In addition, some tests showed a significant difference between a-tDCS and c-tDCS (p < .05). The findings indicated positive effects of both a-tDCS and c-tDCS on the left DLPFC, with more efficacy of a-tDCS on postural stability in LBP patients with HFP.