The purpose of the present study was to extend the knowledge of functional linkages between visual and mental load, performance, and prefrontal cortex (PFC) activity, during forestry forwarding work. Eleven healthy participants, range 21–51 years old, with a minimum of 1-year work experience, carried out the task of loading logs along a standardized path in a machine simulator during two counterbalanced test conditions: (i) conventional crane control, and; (ii) semi-automated crane control. Mental load was assessed by quantification of oxygenated hemoglobin (HbO2) concentration changes over the right dorsolateral prefrontal cortex (dlPFC) via non-invasive functional near infrared spectrometry (fNIRS). Visual, autonomic, and motoric control variables were measured and analyzed in parallel along with the individual level of performance. Linear Mixed Models (LMM) analysis indicated more mental load during conventional crane work. Collectively, our data suggest that fNIRS is a viable tool which can be used in neuroergonomic research to evaluate physiological activity levels in PFC.