In recent years, research has aimed to enhance the environmental friendliness of activated carbon by modifying its surface properties to effectively capture specific harmful gases. This study’s primary goal is to swiftly introduce oxygen functional groups to activated carbon surfaces using microwave and plasma techniques and evaluate their characteristics. In the microwave method, we varied nitric acid concentrations and treatment durations for surface modification. Additionally, plasma treatment was used to introduce oxygen functional groups for comparative purposes. Surface characteristics were assessed through SEM, BET, XPS, and FT-IR analyses. The results indicate that in the microwave method, the quantity of oxygen functional groups increased with longer reaction times. Specifically, the sample treated for 20 min with 8 moles of nitric acid displayed an oxygen content of 14.11 at%, and higher nitric acid concentrations led to a reduced specific surface area. In the case of plasma treatment, higher oxygen flow rates resulted in an O1s content of 17.1 at%, and an increase in oxygen flow rate introduced more oxygen functional groups but decreased the specific surface area.