In today's world of education, a successful teacher can be assumed to be the one who benefits from Task-Based Language Teaching (TBLT), which demands consideration of teachers' beliefs about tasks. The present paper takes into account developing a questionnaire regarding teachers' beliefs about tasks. To this end, 300 English as a Foreign Language (EFL) teachers from Mazandaran province participated in the study. The raw items for the questionnaire were collected by randomly interviewing 15 participant teachers and the related literature on teacher cognition research on TBLT. Then the items were factor-analyzed to develop the final version of the Teachers' Beliefs on Task Questionnaire (TBTQ). Employing Exploratory Factor Analysis (EFA) resulted in a six-factor structure including TBLT and teacher education, TBLT and the learners' expectations, TBLT and challenges with Present-Practice-Produce (PPP) approach, TBLT and teachers' time limitations, TBLT and teachers' characteristics, and the feasibility of TBLT resources. Findings revealed that although TBLT has been considered as an innovative approach due to its inspiration from Communicative Language Teaching (CLT), teachers' attitudes towards TBLT implementation appear to have been taken for granted according to the components emerged from the factor analysis. It is suggested that TBTQ can be used in both foreign and second language contexts in order to identify different categories that can shape teachers' beliefs about tasks and provide further pedagogical insights into designing and implementing tasks more effectively.