Few studies have investigated the changes in patient state index (PSI) and bispectral index (BIS) in response to abrupt increase in electromyographic (EMG) activity. These were performed using intravenous anesthetics or reversal agents for neuromuscular blockade (NMB) other than sugammadex. We compared the changes in BIS and PSI values caused by the sugammadex reversal of NMB during steady-state sevoflurane anesthesia. We enrolled 50 patients with American Society of Anesthesiologists physical status 1 and 2. At the end of the surgery, we administered 2 mg kg⁻¹ sugammadex while maintaining sevoflurane for a 10-min study period. The changes in BIS and PSI from baseline (T₀) to train of four ratio of 90% were not significantly different (median difference 0; 95% CI − 3 to 2; P = 0.83), neither were the changes in BIS and PSI values from T₀ to their maximum values (median difference 1; 95% CI − 1 to 4; P = 0.53). Maximum BIS and PSI were significantly higher than their baseline values (median difference 6; 95% CI 4–9; P < 0.001 and median difference 5; 95% CI 3–6; P < 0.001, respectively). We found weak positive correlations between BIS and BIS-EMG (r = 0.12, P = 0.01), as well as PSI and PSI-EMG (r = 0.25, P < 0.001). Both PSI and BIS were affected to some extent by EMG artifacts after sugammadex administration.