The Islamic State (IS) jihadist group claimed the attack in central Tunis as well as bombings earlier in 2015 at the Bardo National Museum and at a beach resort that killed 59 foreign tourists and a Tunisian guard.
The state of emergency has been in place since the attack, in spite of government assurances that security has improved in the north African nation.
"The security situation is (now) stable," Prime Minister Youssef Chahed told AFP earlier this month. "I would say that we are no more under threat than other countries in the world."
Tunisia, which relies heavily on money generated from tourism, last witnessed a major security incident in March, when dozens of jihadists assaulted state security installations in a town near the border with strife-torn Libya.
That attack killed 13 security forces members and seven civilians, but authorities praised the army and police response which resulted in the deaths of at least 55 jihadists.
A relative calm has since taken hold, and former prime minister Habib Essid in July hailed the first time the Muslim holy month of Ramadan passed without a jihadist incident in Tunisia since 2012.
"We have invested heavily in military equipment and also in human resources to keep the country secure," Chahed said.
European countries and the United States have stepped up cooperation, and President Beji Caid Essebsi has confirmed the presence of 60-70 US instructors for surveillance drones along the Libyan border.
A security official however insisted that the continued state of emergency was justified.
"Terrorist elements are still moving around in the mountains of the west (bordering Algeria) even though the noose is tightening and a certain number of their leaders have been killed," the official said, speaking on condition of anonymity.
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At the start of November, a soldier was killed at his home in the Mount Mghilla area, a key hiding-place of jihadists, in an attack claimed by IS.
The security official said: "Hardly a week goes by without the police dismantling a terrorist cell" or announcing the seizure of weapons and ammunition.
The chaos in Libya alone justifies the state of emergency, according to researcher Rafaa Tabib, an expert on Tunisia's violence-plagued neighbour.
The measure has "helped the security forces in the fight against terrorism. They've been able to carry out raids... and to arrest suspects without judicial warrants."
But rights groups have raised concerns.
It has "limited the freedom of many people placed by the security services under administrative supervision on the slightest suspicion," said Messaoud Romdhani of the Tunisian Human Rights League (LTDH).
Analyst Tarek Belhaj Mohamed said "growing social tensions" in Tunisia, hampered with weak economic growth since its 2011 revolution, were also a factor behind the state of emergency.
In January, a night-time curfew was enforced for several days after unrest in central parts of the country, the worst since the uprising that ousted strongman Zine El Abidine Ben Ali.
Emergency law allows authorities to ban strikes and meetings that might "provoke or maintain disorder", to temporarily close theatres and bars, and to place controls on media output.
At a ceremony on Thursday for the slain presidential guards, Essebsi unveiled a memorial inside the barracks of the presidential security service in a suburb of Tunis, showing three special agents with their weapons.
Twelve gunshots were fired in the air and the president lit two bowls with a flame brought to the barracks from the scene of the bus bombing, 20 kilometres (12 miles) away.