Dengue fever is an extremely common infection in Indonesia, with an estimated 77.96 cases / 100.000 person-years in 2016. However, in 2020 the threat of extremely contagious SARS CoV-2 or COVID-19 in Indonesia emerged, which has infected more than 100.303 persons by July 28, 2020, and expected to grow exponentially except if very strict measures were implemented. There are similar symptoms and laboratory findings with both dengue fever and COVID-19, paving way to dangerous possibilities such as incorrect or delayed initial treatment. This is especially worrisome in the context of the pandemic, where COVID-19 positive patients must be promptly identified, isolated and contact-traced, and eluded diagnosis might possibly endanger communities and healthcare workers. We present cases of patients who initially presented with symptoms and laboratory findings of dengue fever, including positive NS1 and/or IgM serology results. During the course of illness these patients fail to show characteristic dengue symptoms, and two cases begin to show respiratory symptoms. Upon further investigation with chest X-ray or contact tracing, the patients were indicated for COVID-19 swab test, which yielded positive results. Repeat dengue IgM/IgG returned positive in one case, suggesting dengue coinfection; however in all other cases, the repeat testing returned negative, suggesting that the initial serologies were false positives. These cases highlight the importance of comprehensively studying patients with apparent dengue fever symptoms and serology, and using the appropriate adjuvant test according to the course of the disease, since a serological overlap may exist between the two diseases.