Near infrared spectroscopy (NIRS) has been used as a low cost, noninvasive method to measure brain activity. In this paper, we experiment to measure the effects of variables and controls in a source code to the brain activity in program comprehension. The measurement results are evaluated after noise reduction and normalization to statistical analysis. As the result of the experiment, significant differences in brain activity were observed at a task that requires memorizing variables to understand a code snippet. On the other hand, no significant differences between different levels of mental arithmetic tasks were observed. We conclude that the frontal pole reflects workload to short-term memory caused by variables without affected from calculation.