The charity's statement comes after the joint Korean women's ice hockey team and the pro-unification flag show.
Also, the sister of North Korean leader Kim Jong Un shook hands with South Korea's president which also showed an unexpected show of unity in Pyeongchang.
Open Doors has asked people not to forget the thousands of Christians persecuted under the brutal Kim regime.
Dr Matthew Rees, advocacy policy officer at Open Doors, said: "As many nations come together to take part in the Winter Olympics, let us not forget that every day over 300,000 Christians are denied the right to take part in the religious observance of their choice. They are a beleaguered community who are fighting for their very survival."
The belief that God is a higher authority than North Korea's leader, Kim Jong-un, is seen as a threat .
It's lead to tens of thousands of Christians being incarcerated in labour camps, and thousands more keeping their faith in Christ a complete secret.
"They ignore all freedoms," said Timothy, a North Korean refugee. "The human rights level is zero per cent. Religions are not allowed. The leader of North Korea has to be worshipped as god, and this will not change unless the regime collapses."
Open Doors said despite this tremendous persecution, the church in North Korea is growing. The organisation estimates that there are 300,000 Christians in North Korea.
As a way to support North Korean believers and to understand their hardship, pain and courage, Open Doors has asked Christians to live like a North Korean with their Lent resource of the same name.
The charity said: "Daily Bible readings, prayers and actions help you to experience a little of what North Korean Christians endure every day. You might end up buying your Bible or surviving a day without electricity.
"These actions cannot replicate the reality of our dear brothers and sisters, but with prayerful reflection they can provide a window into the world of a North Korean Christian."
North Korea is number one on the 2018 Open Doors World Watch List, which ranks 50 countries where it's the most difficult to live as a Christian.
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