Anti-Asian racism is a public health concern, and it has escalated during the coronavirus disease 2019 (COVID-19) outbreak. Bystanders—individuals who directly witness or become aware of acts of racism—can help by discouraging perpetrations of discrimination (and other forms of violence), offering help and support to victims, and reinforcing antiracist prosocial norms. Yet, little is known about who engages in antiracist bystander interventions in response to discriminatory events, and who engages in proactive bystander behaviors to discourage future acts of racism. In the current study, 456 US community adults of diverse ethnoracial backgrounds (18-85 years, Mage = 48.8, 52.0% women, 212 Asian Americans) reported on their experiences with discrimination, attitudes about the acceptability of discrimination, and engagement in proactive and reactive bystander behaviors. About 40% of the Asian American participants experienced discrimination during a one-week period in early months of the COVID-19 pandemic. Among individuals who witnessed anti-Asian discrimination during the study period, 45% of them engaged in antiracist reactive bystander interventions. Controlling for ethnicity, gender, and attitudes about the acceptability of discrimination, individuals who reported more frequent experiences with everyday discrimination prior to the pandemic were more likely to engage in reactive bystander behaviors in response to anti-Asian discrimination. Lifetime experiences with discrimination may contribute to individuals’ active engagement in antiracist bystander behaviors. Future research directions on antiracist bystander actions and allyship are discussed.