Open Doors is highlighting how the period of prayer and fasting presents "multiple challenges" for believers in areas such as the Arab Peninsula.
The organisation, which serves persecuted Christians across the globe, is urging believers to use their 30 Days of Prayer resource.
One Open Doors worker in Egypt said: "As much excitement as the Islamic holy month brings to Muslims, it does carry a great deal of burdens and concerns to the Christian community in Egypt.
"It is a very long 30 days during which Christians in schools, work or public spaces will receive harsh looks and verbal harassments from fanatic Muslims because of their faith.
"Even in some cases, Christians may face physical violence due to the fact that they were caught eating their lunch by their fasting Muslim co-workers or neighbours!"
During Ramadan, Muslims are forbidden from eating, drinking, smoking or having sexual relations between dawn and sunset.
One Christian in Oman told Open Doors: "We pray for Muslims to see the truth and receive visions and dreams of Jesus. Each year we hear testimonies of that actually happening. They see Jesus dressed in white clothes."
Meanwhile, the Archbishop of Canterbury Most Rev Justin Welby took to Twitter, saying he was "wishing all observing #Ramadan in the UK and around the world Ramadan Kareem!"