Language teaching moved to online learning due to the Coronavirus outbreak. This study was carried out to describe the correlation between students' self-efficacy levels, motivation, attitude, and anxiety across proficiency levels, the difference between the four affective factors across proficiency levels, and how these affective factors affect students' performance in an online writing module or emergency remote teaching. Eighty-one students taking a paragraph writing course participated in the study and were divided into high, moderate, and low proficiency levels. Four sets of questionnaires inquiring about the students' affective factors and writing scores were used as the main data sources. ANOVA was performed to compare the level of the four affective factors. The results showed that only motivation is at a high level, while the levels of self-efficacy, attitude and anxiety are at a moderate level. Among the affective factors, the levels of self-efficacy and motivation are significantly different across proficiency levels, while attitude and anxiety are not. Further, the result of the simultaneous analysis showed that among the four affective factors, only motivation was found to have a significant effect on students' performance in the online writing class module. The findings of this study illustrate that writing teachers have the responsibility to create a non-threatening classroom atmosphere as an alternative way to increase students' writing motivation.