Background: The coronavirus disease 2019 (COVID-19) omicron (B.1.1.529) variant reduced the risk of severe disease compared with the original strain and other variants, but it appeared to be highly infectious, which resulted in an exponential increase in confirmed cases in South Korea. As the number of confirmed cases increased, so did the number of pediatric patients’ hospitalization. This study aims to evaluate the frequency and clinical features of febrile seizure associated with the COVID-19 omicron variant in children. Methods: We retrospectively reviewed the medical records of children aged under 18 years with febrile seizure who were tested for COVID-19 from February 2020 to April 2022 at Ajou University Hospital, South Korea. Based on the dominant variants, we divided the period into the pre-omicron (from February 2020 to December 2021) and omicron periods (from January 2022 to April 2022) and compared the clinical characteristics between the two. Also, we compared the clinical characteristics of febrile seizure between COVID-19 positive and negative group during the omicron period. Results: Among the 308 children, 211 patients (9.2 patients/months) and 97 patients (24.3 patients/months) were grouped into pre-omicron and omicron periods, respectively.Compared with the pre-omicron period, patients in the omicron period showed significantly higher mean age (pre-omicron vs. omicron, 22.0 vs. 28.0 months; P = 0.004) and COVID-19 positive results (pre-omicron vs. omicron, 0.5% vs. 62.9%; P < 0.001). As the COVID-19 confirmed cases in the omicron period increased, the number of COVID-19 associated febrile seizure also increased. In the omicron period, 61 children were confirmed to be positive for COVID-19, and COVID-19 positive group showed statistically significant higher mean age (positive vs. negative, 33.0 vs. 23.0 months; P= 0.003) and peak body temperature than the negative group (positive vs. negative, 39.1°C vs. 38.6°C; P = 0.030). Despite the lack of significance, COVID-19 positive group showed longer seizure time, multiple seizure episodes, and higher prevalence of complex febrile seizure. Conclusion The frequency of COVID-19 associated febrile seizure increased in the omicron periods. In addition, in this period, children with febrile seizure diagnosed with COVID-19 had a higher mean age and higher peak body temperature.