The New York-based rights group called on Catherine Ashton to condemn the sentences.
The activists from Eastern Province were handed jail terms ranging from five to 10 for posting messages on Facebook calling for mass protests, according the HRW.
"Sending people off to years in prison for peaceful Facebook posts sends a strong message that there's no safe way to speak out in Saudi Arabia, even on online social networks," Joe Stork, HRW's deputy Middle East director, said in a statement.
"If the EU doesn't raise these cases with Saudi officials this weekend, its silence will look like craven compliance with the rights abuses of an authoritarian state."
Saudi Interior Ministry officials were not immediately available for comment.
A Saudi-based human rights campaigner said the activists were all from al-Ahsa governorate who had set up Facebook pages to urge people to stage demonstrations.
Human Rights Watch said the seven men were detained in September 2011 and had spent a year and a half in prison before being tried by a special tribunal set up in 2008 to handle terrorism-related cases.
The court did not charge the men with directly participating in the protests, HRW said, rather with inciting "protests, illegal gathering, and breaking allegiance with the king".
But discontent lingers on with protests in eastern Saudi Arabia, where at least 20 people have been killed by security forces since 2011.
On Thursday, thousands protested against the kingdom's ruling al-Saud family at the funeral of a man shot dead by police, an incident that ended months of relative calm in the province.
Saudi officials in the past came under fire for charging other prominent activists under breaking the kingdom’s law.
On June 17, Saudis sentenced 58-year old Mikhlif al-Shammari to five years for his political writings.
"Al-Shammari is the latest in a lengthening line of Saudi human rights activists hauled before the courts and branded as criminals for exercising their right to free speech," according to Joe Stork, the HRW's deputy Middle East director.
Shammari was arrested in 2010 allegedly for “sowing discord” and other offences.
More than 40,000 political prisoners, mostly prisoners of conscience, are reportedly in jails across Saudi Arabia.