Brucellosis is a infectious zoonosis with important health and economic impacts, both for animal production and public health. We aimed to determine the prevalence of brucellosis in beef cattle in the microregions of Araguaína and Bico do Papagaio in northern Tocantins and to verify whether there are post-mortem changes suggestive of brucellosis in the carcasses. A total of 2,871 serum samples (2,203 males and 668 females) were collected in the municipality of Araguaína between October and November 2019, from 76 beef cattle herds in 25 municipalities in the north of Tocantins. The screening for buffered acidified plate antigen test (BAPA) and confirmation test for 2-mercaptoethanol (2-ME) were conducted as recommended by the Brazilian Ministry of Agriculture, Livestock, and Supply (MAPA). Of the samples, 37.31% were reactive in the BAPA test, and of these, 26.24% were confirmed for 2-ME. Thus, 9.79% (281) of the total evaluated samples tested positive for the presence of brucellosis. The prevalence in males and females was 6.45% (142) and 20.81% (139), respectively. Among the herds evaluated, 77.6% (59) had at least one individual test positive for brucellosis, and at least one herd tested positive in each of the 25 municipalities sampled. As this study evaluated animals in a slaughterhouse, the higher prevalence of positive females may have been related to the disposal of animals with reproductive problems. There was no significant difference in the prevalence of brucellosis in slaughter cattle between the microregions evaluated (p > 0.05). No animals were reagent for brucellosis in ante-mortem documentation, and no anatomopathological changes suggestive of brucellosis were observed during post-mortem inspection. The most frequent post-mortem findings were contamination (43.91%), blood aspiration (17.36%), and pulmonary emphysema (15.98%). Considering the official results of the monitoring programs of the state of Tocantins and previous studies, post-mortem macroscopic inspection of carcasses may not be enough to detect animals with this zoonosis, and it may be necessary to take measures to promote animal and public health.