During the COVID-19 pandemic, K-12 face-to-face teaching shifted to online teaching. Many teachers faced challenges in preparing and delivering their content online due to a lack of training and experience. This study examined the relationship between K-12 teachers' teaching self-efficacy and their perceptions toward using Learning Management Systems to teach online during the pandemic. One hundred and forty-one usable responses were analyzed using Structural Equation Model. Results indicated that the levels of support teachers received and their beliefs about the Learning Management System had a direct impact on their self-efficacy in online teaching. Future research can focus on identifying the pedagogies used to ensure the quality of online teaching and how professional development can improve teachers' online teaching self-efficacy.