John 1:18 (NIV) No one has ever seen God, but the one and only Son, who is himself God and is in closest relationship with the Father, has made him known.
John 1:18 (NKJV) No one has seen God at any time. The only begotten Son, who is in the bosom of the Father, He has declared Him.
John 1:18 (NLV) The much-loved Son is beside the Father. No man has ever seen God. But Christ has made God known to us.
John 1:18 (RSV) No one has ever seen God; the only Son, who is in the bosom of the Father, he has made him known.
John 1:18 (YLT) God no one hath ever seen; the only begotten Son, who is on the bosom of the Father -- he did declare.
The NIV, in this passage is demonstrating a bias of the translators in favour of the doctrine of the Trinity which is false. They have actually changed scripture to suit their preconceptions. This is clearly wrong. They have done this elsewhere as well causing some people to call the NIV the "New Inaccurate Version."
The last version quoted in my list is "Young's Literal Translation (YLT). This version is very accurate and translates the actual Greek text word for word. You can see from that version what a great disservice has been done by the translators of the NIV in this verse.
I hope you have found this helpful.