<p>Although considerable research has explored the role of feedback in second language writing, limited studies have compared the effects of AI-generated feedback and teacher-written feedback on both academic performance and emotional experience, particularly in EFL contexts. This mixed-methods brief report investigated the impact of AI-mediated feedback on Iranian EFL learners’ writing achievement and perceptions. Twenty-two upper-intermediate institute students were randomly assigned to either an AI feedback group (<i>n</i> = 11) or a teacher feedback group (<i>n</i> = 11). Both groups completed two parallel opinion paragraph writing tasks and received feedback accordingly. Quantitative analysis showed that the AI feedback group achieved significantly greater improvement in post-test scores than the teacher feedback group, highlighting the role of automated formative feedback in enhancing writing performance. Qualitative thematic analysis revealed that AI feedback promoted clarity, autonomy, and motivation, whereas teacher feedback provided emotional reassurance and interpersonal support. These findings suggest that AI systems, when designed and implemented thoughtfully, can complement human feedback by fostering both linguistic progress and learner autonomy in EFL writing instruction.</p>