The present study aims to explore the effects of a single session of attentional bias modification training at the behavioural and physiological levels. Healthy participants (n = 132) were allocated by means of a double-blind randomization into a trained group and a control group. The paradigm consists of a dot-probe task, using emotional facial expressions, during which participants had to discriminate two letters. Autonomic changes were assessed by subtracting recovery period data (recorded during a two-minutes period after the task) from baseline period data (recorded during a two-minutes period before the task). Trained participants’ correct detection rate significantly improved throughout the task, indicating a better performance towards its end. Such a result was not observed in the control group. This means that trained participants allocated significantly more attention towards the positive stimuli at the end of the task compared to its beginning. HF-HRV peaks were significantly higher during the recovery period than during the baseline period, only for trained participants. A significant correlation between LF-HRV data and participants' tendency to use positive refocus strategies when faced with a stressful event was also observed. These results show that a dot-probe task can be used to modify attentional biases, and that such a training seem to increase parasympathetic influence. The task's effect on physiological activity seem to be influenced by emotional regulation strategies.