Some think the Church today is the Kingdom of God. Although there is a connection between the two, they are not identical. Jesus Christ is the Head of the Church (Ephesians 1:22), which is the body of believers called by God now to proclaim the good news of the coming Kingdom of God.
Christ rules His Church, thus it is under His royal power. We might say the Church is the forerunner of the coming Kingdom of God. Or, as Jesus Christ said, the Kingdom of God is like the proverbial mustard seed, waiting to grow rapidly at Jesus' return (Matthew 13:31-32).
The Bible, however, doesn’t use the word kingdom to apply directly to the Church. Instead, the Kingdom of God refers to God's prophesied government, which will literally rule this on this earth (Revelation 11:15; Revelation 5:10). The Kingdom of God is not here yet.