Sarawak, a state in Malaysian Borneo, has never reported a case of Zika virus (ZIKV) infection nor conducted any seroprevalence studies on the virus. This study aimed to provide a serological insight into ZIKV in Sarawak. 212 sera samples collected from a dengue surveillance study conducted from 2007 to 2011 were retrospectively analyzed. Samples negative for both dengue and Japanese encephalitis virus by RT-PCR were screened by immunoblots assay for ZIKV prM protein. Positive samples were further subjected to 50% plaque reduction neutralization test (PRNT50) for confirmation. 20 (9.4%) sera samples were positive for ZIKV prM protein but not against prM of dengue and Japanese encephalitis virus. These 20 samples were further subjected to PRNT50, and six samples (2.8%) showed possible seropositivity for ZIKV. This preliminary investigation provides serological evidence of ZIKV infection in Sarawak and highlights the importance of conducting surveillance programs for ZIKV in this dengue-endemic state.