Starting with the conventional thermal-converter-based square-law approach for alternating current (AC) power measurement schemes, this paper discusses how to realize a broadband AC active power standard using thermal converters, and explores the performance of thermal-converter-based AC power meter in presence of harmonics. Two measurement schemes for broadband AC power metering based on thermal converters are proposed, and it is demonstrated that the fundamental power and harmonic power is possible to be measured under the condition that voltage and current contain harmonic component, and its application range is easy to expand. Compared to the traditional sampling method, the proposed scheme has merits of high accuracy and low cost for the high-frequency power measurement, e.g. in the kHz~1MHz range.