Similar symptoms and laboratory findings between dengue and coronavirus disease 2019 (COVID-19) pose a diagnostic challenge in some dengue-endemic countries in Asia. In this study, we reported three cases of suspected COVID-19-dengue co-infection in hospitals of Bali, Indonesia. Serological data demonstrated that patients with positive results on dengue virus (DENV) NS1 antigen and anti-dengue IgM were also reactive to COVID-19 rapid antibody tests, suggesting dengue-COVID-19 co-infection. However, two patients were later confirmed negative for SARS-CoV-2 by qRT-PCR, implying a plausible cross-reactivity of anti-dengue and anti-COVID-19 antibodies in the serological test. Co-infection of dengue and COVID-19 was evident in one patient, following confirmation of SARS-CoV-2 by qRT-PCR and DENV infection using NS1 antigen serology test. This case was the first case of dengue and COVID-19 co-infection in Indonesia and at the same time revealed possible cross-reactivity between SARS-CoV-2 and DENV antibodies based on rapid serological tests. Our study shall raise public health concern for COVID-19 and dengue detection in Indonesia as well as in other dengue-endemic countries as it may present a tip of the dangerous iceberg for the nationsâ€™ effort to manage of both pathogens.