The New York-based rights group urged EU foreign policy chief Catherine Ashton and other European officials who were meeting with Gulf counterparts, including Saudi Arabia, in Manama on Sunday to condemn the convictions.
Eastern Province has seen occasional protests by minority Shia Muslims over the past two years against alleged discrimination and negligence, which the Riyadh government denies.
"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 Shia from al-Ahsa governorate who had set up Facebook pages to urge people to stage demonstrations.
"The sectarian situation in the region made the sentences tough and
unreasonable," he said, speaking on condition of anonymity.
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".
Saudi Arabia swiftly moved in early 2011 to quell protests by minority Shia Muslims over the deployment of Saudi forces to nearby Bahrain to help crush anti-government demonstrations there.
A majority of Bahraini citizens are Shia.
But discontent lingers on with occasional protests in eastern Saudi Arabia, where at least 20 people have been killed by security forces since 2011.
On Thursday, thousands of Shia Muslims protested against the kingdom's ruling al-Saud family at the funeral of a wanted man shot dead by police, an incident that ended months of relative calm in the province.
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@ali: what about NATO, Saudi, Turkey and Qatari funding for the genocide of everyone since the Free Syrian Army has Alqaeda elements in it who'll make it another Afghanistan! Another peaceful country ruled by a secular dictator overthrown and left to rot. Down with Saudi!
If u r shia ur posts are always allowed on et but Try criticizing Iran for the génocide of sunni muslims in syria
The real enemy of Muslim Ummah! Down with the House of Saud! I hope I get to see revolution-French style-in Saudi Arabia in my lifetime then the muslim world will finally be at peace with itself with no more export of Wahhabi Islam. We should make friends with Israelis and Indians and throw out Saudi Arabia out of Pakistan for good! We can learn a lot more technologically from Israel than Saudi Arabia which is just filled with barbarians who have suffocated not only their own country but continously support anti-progress parties everywhere in the muslim world. I hope Mecca/Medina become like a Vatican state with no control from Saudi. They belong to the entire Muslim world.
Saudis are creating trouble in Syria and financing trouble makers all over world. Time for pay back now. Time to expose unholy Saudi-American alliance.