Many rights groups have called for the closure of the US camp in Cuba.
Irene Khan, the secretary-general of Amnesty International, said in a statement: "Guantanamo is an anomaly that must immediately be corrected and the only way to do so is by closing it down."
Protests are expected in many other countries, including Britain and the US.
Nearly 800 people from over 20 different countries have been held in the Guantanamo Bay facility since 2002.
The US has suggested it wants to close Guantanamo, but about 275 detainees remain there, including about 60 who US military panels have cleared for release or transfer.
Sami al-Hajj an Al Jazeera cameraman, is among those still imprisoned.
Zachary Katznelson, senior counsel at Reprieve - an organisation that provides legal assistance to prisoners - said the US approach to those imprisoned in Guantanamo is inconsistent.
"On the one hand, [the US is] continuing to try and paint the people in Guantanamo, even though they haven't been charged and they haven't been tried, as vicious terrorists," he said, "And at the same time [they are] trying desperately to get other countries to take them in."
At the same time, some countries will not accept prisoners that Washington no longer wants to hold, and in some cases detainees themselves do not want to be sent back because they fear persecution.
Guantanamo has been extremely controversial and analysts say it has damaged the US reputation abroad.
In December last year, Martin Scheinin, a UN special rapporteur on human rights, said he strongly suspected the CIA of using torture on inmates.
He also suggested that many were not being prosecuted to keep the abuse from being revealed.
Friday marks the sixth year since the first prisoners were transferred to Guantanamo.
In that time, four prisoners have committed suicide by hanging, three in June 2006 and one in May 2007.
A fifth prisoner died of colorectal cancer in December 2007, the first to die of natural causes.
A number of other prisoners are on hunger strike.