A human chain will be formed on Cairo's Qasr El-Aini bridge to highlight the plight of thousands of civilians facing military trials.
The event, called 'Release', will take place at 10pm on Friday.
The No to Military Trials for Civilians group has said its members will attend the event.
The event's organisers said that the human chain is to remember all the activists detained since the January 25 revolution.
"The detainees are fasting in Ramadan without even a fan, and are eating an Iftar that is unfit for human beings. Show them your gratitude, if only through standing in the shade after Iftar for an hour."
According to the official 'Release' Facebook page, the human chain is to show solidarity with people facing both criminal and political trials in military courts.
Among the groups taking part in the event are Salafyo Costa (moderate Salafists), No to Military Trials for Civilians and the April 6 Youth Movement in Suez.
A military court on Thursday imposed the first jail sentence on activists since the January 2011 uprising.
Reda Mohamed, a female activist, received a three-month sentence, whilst Nesrine Youssef and Hayat Hussein received six-month sentences.
The three activists were arrested on 4 May, along with sixteen others, during the Abbasiya clashes.
Activists have called on President Mohamed Morsi to immediately end military trials for civilians and to issue an amnesty and pay compensation to those who were tried in military courts.
Last week, Morsi ordered the release of 572 people detained by the military since last year's uprising, including 530 who had already been convicted.
Morsi's order was issued on the recommendation of a committee recently drawn up by the president to look into all cases of civilians detained by military authorities.
A total of 11,879 Egyptians have been detained by the military since last year's uprising, according to figures issued by the committee.
Of these, 9,714 have since been released.