The amplitude of the error-related negativity (ERN) is known to be correlated with attention to task and general cognitive control abilities. Yet, previous research has struggled to consistently link ERN amplitude with behavioral accuracy or reaction time in the task from which the ERN is being measured. This lack of relationship could be due to many factors that are difficult to control for, so explorations of other converging measures to understand error processing and subsequent behavior adjustment are warranted. The current study examines how two other physiological markers of error processing—the phasic pupillary response (PDR) and the positivity following an error (Pe)— relate to post-error behavior. Additionally, we also examine relationships between the three physiological indices of error-processing. In the study, EEG and pupillometry were simultaneously recorded while participants completed 12 blocks (50 trials each) of an Erickson Flanker task. For post-error accuracy, we found that on a single trial level, the amplitude all three physiological error processing indices for error trials predicted whether participants made a correct response on the following trials. At the subject level, only the PDR predicted average post-error accuracy. For post-error slowing, at the single trial level, only the Pe predicted post-error slowing, whereas only the ERN predicted post-error slowing at the subject level. This suggests that the PDR and Pe might represent promising indicators of post-error behavior adjustment, and also highlights the need to examine relationships at multiple levels of analysis. We also found that both the ERN and Pe correlated with PDR amplitude. Results are discussed.