Are there some people on the earth when Cain killed Abel?

Yes, according to the Bible, after Cain killed Abel, he was banished by God to wander the earth. It is believed that there were other people living on the earth at that time, as Cain later went on to build a city and have descendants.

Yes, there were other people on Earth when Cain killed Abel. According to the Book of Genesis, after Cain killed Abel, God banished Cain to the land of Nod, where he encountered other people who had descended from Adam and Eve.