Abstract Introduction Few instruments are available in Brazil to evaluate psychomotor activity in psychiatric emergency, clinical, and research settings. This study aimed to perform a cross-cultural adaptation of the Behavioral Activity Rating Scale (BARS) into Brazilian Portuguese and assess the adapted scale’s psychometric properties. Method An expert consensus committee conducted a translation and back-translation of the original scale, resulting in the BARS-BR. Four pairs of physicians administered the BARS-BR and the Sedation-Agitation Scale (SAS) to patients in a hospital psychiatry emergency room and patients in the hospital’s psychiatric wards. The BARS-BR was compared to the SAS to assess concurrent validity and internal consistency was evaluated with the Bland-Altman technique. Results In the emergency room, the correlation coefficients between the first and second assessments were rho = 0.997 and rho = 1.0, respectively. In the hospital wards, the correlation coefficient between the pair of evaluators was rho = 0.951. There were strong correlations between the BARS-BR score of the first examiner and the SAS score of the second examiner (rho = 0.903) and between the SAS score of the first examiner and the BARS-BR score of the second examiner (rho = 0.893). Conclusion The BARS-BR showed good psychometric properties, and we recommend its use because it constitutes an easy method for assessment of changes in psychomotor activity. Further studies are suggested to evaluate adoption and comprehension of the BARS-BR scale by all classes of healthcare professionals.