Learners of English as a foreign language (EFL) face various challenges which impede their efforts to achieve English proficiency, especially in speaking performance. In response, this study sets out to use the Flipped Classroom Model (FCM) as a teaching method to investigate the effectiveness of the FCM on EFL learners' anxiety in English speaking performance. A mixedmethods research design was utilized whereby 27 Omani undergraduate students majoring in English as a foreign language at Buraimi University College (BUC), Sultanate of Oman were selected purposively as the subjects of the study. The collected data involved the Anxiety in English Speaking Performance Questionnaire (AESPQ) that was distributed in three stages: pre, midway and post the implementation of FCM. Another set of data was elicited in the focus group interviews and students' reflective journals. Findings indicated that after twelve weeks of using FCM, a considerable improvement occurred on EFL learners' anxiety in English speaking performance across time. The results of the One-way ANOVA showed that there were significant differences among the EFL learners' levels of anxiety in speaking English, F (?, ??) = 111.492, P0.001, ?2= 0.811), and MANOVA results revealed that there was a significant difference between the four dimensions of AESPQ over time (Wilks Lambda =0.017, F= 134.718, h2=0.983). FCM was found to be appropriate to all the students in this study since it satisfied their needs and suited their learning styles. Essentially, the findings reported in this research would contribute to advancing English language teaching, not only in instructional design but also in promoting EFL instructors to be more interested in using FCM.