Two international guidelines/standards for human protection against electromagnetic fields are currently undergoing revision. The main revision would be on the metric and limits above the transition frequency; 3 GHz in IEEE C95.1 Standard and 10 GHz in International Commission on Non-Ionizing Radiation Protection. The frequency from the 3–10 GHz to 300 GHz includes the frequency band, which will be assigned for the fifth generation (5G) wireless communication system. Even though metrics and limits in the current guidelines/standards were different, they may be harmonized in part based on recent dosimetry research, as shown in draft guidelines/standard. This study reviews the rational for the undergoing revision, especially above 6 GHz from engineering viewpoint.