Because functional near-infrared spectroscopy (fNIRS) eases many of the restrictions of other brain sensors, it has potential to open up new possibilities for HCI research. From our experience using fNIRS technology for HCI, we identify several considerations and provide guidelines for using fNIRS in realistic HCI laboratory settings. We empirically examine whether typical human behavior (e.g. head and facial movement) or computer interaction (e.g. keyboard and mouse usage) interfere with brain measurement using fNIRS. Based on the results of our study, we establish which physical behaviors inherent in computer usage interfere with accurate fNIRS sensing of cognitive state information, which can be corrected in data analysis, and which are acceptable. With these findings, we hope to facilitate further adoption of fNIRS brain sensing technology in HCI research. ACM Classification: H5.2 [Information interfaces and presentation]: User Interfaces. - Graphical user interfaces. General term...