Foreign language anxiety (FLA) has extensively been reported to interfere with second language learning and performance. To mitigate anxiety, researchers have called for the inclusion of technology into foreign language classes and providing learners with corrective feedback on their performance. One factor that may affect the comprehensibility of such feedback is whether it is carried out through the learners' first language (L1) or second language (L2). As a preliminary endeavour, the present study employed a sequential explanatory mixed-methods approach to investigate the effects of using L1, as compared with L2, during mobile-assisted oral peer feedback (OPF) on speaking performance and anxiety of 32 Iranian English as a foreign language (EFL) learners. To shed further light on the initial findings, semi-structured individual interviews were conducted with 23 volunteered participants. The results verified the significant advantage of L1 OPF over L2 OPF in lowering the participants' FLA within a computer-mediated communication (CMC) context. Mobile-assisted OPF was also deemed efficacious in enhancing the participants' oral proficiency, self-confidence, willingness to communicate, risk-taking, engagement, and self-directed performance.