Artificial intelligence (AI) education is increasingly being recognized as essential at the K-12 level. For better understanding teachers' preparedness for AI education and effectively developing relevant teacher training programs, teachers' technological pedagogical content knowledge (TPACK) readiness and attitudes toward AI teaching must be determined. However, limited research has been conducted on this topic. To address this research gap, we recruited 1,664 K-12 teachers to obtain a comprehensive view of teachers' readiness for and attitudes toward teaching AI in K-12 classrooms. These teachers differed in terms of their gender, teaching subject, teaching grade, teaching experience, and experience in teaching AI. The findings of this study indicated that a substantial gap exists in the AI-related content and technological knowledge of the recruited teachers. Moreover, intriguing relationships were found between the teachers' pedagogical knowledge, content knowledge, and attitudes toward teaching AI. The effects of demographic factors on the teachers' TPACK and attitudes were also examined. On the basis of the findings of this study, recommendations were formulated for developing effective teacher professional development programs in the field of AI education.