We utilized Near-Infrared (NIR) spectroscopy to closely investigate the activation change in anterior prefrontal cortex (aPFC) during verbal anagram problem-solving and learning. We used a parametric design of anagram-solving with three difficulty levels and evaluated anagram skill with two sets of subjects and protocols. The first protocol was a one-time evaluation of untrained subjects (n = 10) and the second protocol evaluated subjects over 6 weeks of training (n = 6). The untrained subjects in the first protocol demonstrated blood oxygenation corresponding to neuronal activation in the aPFC in response to medium and hard difficulty levels of the stimuli, while the easy anagram task deoxygenated the aPFC bilaterally, corresponding to deactivation. Higher performers have more aPFC activation than lower performers in the medium difficulty level anagram-solving task. Six weeks of training in the second protocol showed that training reduced oxygenation in aPFC. In particular, subjects with lower baseline skill in anagram production showed a larger reduction in oxygenation where true performance gains occurred (medium difficulty) and smaller reduction where the performance gains were limited (hard anagrams). Association of the aPFC activation with the difficulty of the complex task suggests that aPFC is a part of a circuit for execution of task performance. In addition, more use of aPFC by untrained high performers suggests that the role of the aPFC is to increase efficiency of a problem-solving task. Thus, the NIR spectroscopy showed that the aPFC is a key structure in the circuit implementing the development of anagram skill.