Working memory is regarded as a cognitive system with limited capacity, which is responsible for saving, manipulating, and remembering online information. The cognitive functions of the brain, such as language, understanding, planning, reasoning, and problem-solving, need working memory. Based on the previous studies, working memory is considered as a central function of frontal brain lobe. Among several protocols on assessing working memory function, the n-back task is regarded as one of the most common ones in the functional imaging studies of working memory. Functional near-infrared spectroscopy (fNIRS) is an optical imaging method for evaluating brain function, which measures nervous activities and hemodynamic response in the cerebral cortex. The present study aimed to assess functional connectivity in frontal brain lobe during conducting dual n-back task at three levels of memory loading (n = 0, 1, 2) by using fNIRS signals. The statistical population included 29 healthy volunteers, among which 11 and 18 ones were left- and right-handed, respectively. They performed a dual n-back task, and the change in the concentrations of Hb and HbO2 was measured by using 24 fNIRS channels existing in the frontal lobe. The matrix of functional connectivity was extracted and evaluated by using partial correlation criterion for all participants and each of right- and left-handed groups at every level of memory loading separately. The statistical analyses of Hb and HbO2 signals (p < 0.05) in each group represented the presence of a bilateral connection between two hemispheres and local connection ones between different areas in each hemisphere with more connectivity in the right hemisphere of the frontal cerebral cortex during conducting the dual n-back task. Based on the comparison of the results related to left- and right-handed groups, a difference was observed between their functional connectivity in some areas, as well as the number of connectivity between various areas. Right-handed participants more utilized the lateralization of the right hemisphere to perform task compared to left-handed did, while left-handed ones represented the decrease in lateralizing or distributing bilaterally in hemispheres, by indicating the difference between some of the brain connectivity were different in these participants by considering the dominance of one of the hemispheres in each of these two groups. In general, the results of the present study demonstrated that fNIRS data is considered as appropriate for assessing the functional connectivity between the different areas of the frontal cerebral cortex during conducting the working memory-related tasks.