Known as what educational contexts do not teach, null curriculum has been considered one of the most significant types of curricula due to its absence, being left out or overlooked. This non-existent curriculum brings an important theoretical tool to the field of curriculum development for the idea that something which is not offered to students has an educational significance and effect. To follow the purpose of the study which is teachers' perspectives on the null curriculum at the BA level, 300 university instructors were selected to participate in this study. To answer the research questions various statistical methods (one-way ANOVA, independent sample t-test, Confirmatory Factor Analysis and Scheffe’s test) have been utilized. Results of this quantitative study revealed that among the sub-constructs of the 21st century, critical thinking, collaboration skills, creativity and innovation skills, self-direction skills, technological literacy, global and local connection skills, economic and financial literacy, business and entrepreneurial literacy and media literacy should be considered as aspects of the null curriculum in TEFL curriculum in BA level in Iran, and they should be added to the present curriculum,however, communication skills are not regarded as aspects of null. In addition, Iranian EFL university instructors’ ratings on different components of 21st-century skills as one aspect of the null curriculum significantly differed. Finally, a model was proposed to describe the relationship between the ratings of the components of 21st-century skills as one aspect of the null curriculum by Iranian EFL university instructors. The findings of the present study can help to a better understanding of the ELT curriculum, aspects of the null curriculum, and 21st-century skills in the Iranian context.