Background Anxiety is one of the most prevalent mental health problems during pregnancy which result in various maternal and newborn complications affecting the health and well-being of the mother and the baby. In countries like Ethiopia, anxiety among pregnant women was not well explored, limiting the development of informed interventions. Thus, this research aims to assess the magnitude of anxiety and associated factors among pregnant women visiting ANC at public health centers in Addis Ababa, Ethiopia. Method We conducted an institutional-based cross-sectional study. Pregnant women who visited antenatal care (ANC) from April 1–14, 2021, were recruited from seven public health centers in Addis Ababa, Ethiopia. Data were collected using a structured questionnaire by trained data collectors. Poisson regression with a robust error variance estimate was used to calculate the prevalence ratio to identify the associated factors; the results were presented with an adjusted prevalence ratio (APR) and a 95% CI. Result A total of 323 pregnant women were recruited from the ANC clinics of public health centers in Addis Ababa. The overall prevalence of anxiety disorder was 12.70%, 95% CI (9.00%–16.10%). The prevalence risk of anxiety was higher among women who reported unplanned pregnancy compared to those who had planned pregnancy (APR 1.99, CI 1.04–3.81), and being single was associated with a higher prevalence risk than being married (APR 2.29, CI 1.14–4.59). Conclusion More than 1 in 10 women had anxiety during pregnancy. The prevalence of anxiety was about two-fold higher among single mothers and among mothers who had an unplanned pregnancy. The study suggests the importance of integrated mental health assessment and services in regular antenatal care, with an emphasis on identifying and caring for women at a disadvantage due to social and obstetric factors.