Who Were the False Teachers?
The false teachers that had come to Ephesus were most likely like those who came to Antioch in Acts. They placed a heavy emphasis on Old Testament Law and circumcision:
Acts 15:1
Some men came down from Judea and taught the brothers, "Unless you are circumcised after the custom of Moses, you can't be saved."
Their teachings were theologically sophisticated and they used Old Testament Scriptures to support their arguments. Given the anti-Pharisee view of the New Testament Scriptures, I think it is safe to assume the false teachers were Pharisees or some type of teachers of the Law.