ORF3a is an accessory protein expressed by all human pathogen coronaviruses and is the only accessory protein that strongly affects viral fitness. Its deletion reduces severity in both alpha- and beta-coronaviruses, demonstrating a conserved function across the superfamily. Initially regarded as a non-selective cation channel, ORF3a's function is now disputed. Here, we show that ORF3a from SARS, but not SARS-CoV-2, promotes potassium conductance in a yeast model system commonly used to study potassium channels. ORF3a-mediated potassium conductance is also sensitive to inhibitors, including emodin, carbamazepine, and nifedipine. This model may be used in future studies on ORF3a and related proteins.