The major objective was to measure the trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) equivalent antioxidant capacity (TEAC) of carbazole derivatives (Ar2NHs) by means of scavenging 2,2′-diphenyl-1-picrylhydrazyl (DPPH) and the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) radical cation (ABTS+·). The Ar2NHs included phenoxazine (PozNH), phenothiazine (PtzNH), iminostilbene (IsbNH) and diphenylamine (DpaNH), and the TEAC of trolox, α-tocopherol (TocH), l-ascorbic acid (VC) and l-ascorbyl-6-laurate (VC-12) were measured as well. The TEAC results revealed that the ability to scavenge DPPH (PozNH > IsbNH ~PtzNH ~TroH ~TocH ~VC ~VC12), differed from the ability to scavenge ABTS+ (PtzNH > IsbNH > PozNH > DpaNH ~TroH ~TocH ~VC ~VC12). CazNH did not react with DPPH and ABTS+·. Furthermore, the addition of acetic acid accelerated the reaction rate of Ar2NH to scavenge DPPH, suggesting that a sequential proton loss electron transfer (SPLET) mechanism occurred with amine-type antioxidants during the trapping of DPPH. In contrast, the addition of acetic acid or pyridine reduced the reaction rate of Ar2NH to scavenge ABTS+., suggesting that the hydrogen atom transfer (HAT) mechanism is the basis for the reaction that is occurring.