The arrest came just days after President John Magufuli ordered officials to take action against "incitement of violence."
Tanzanian opposition number two Tundu Lissu was arrested on Thursday, three days after having called President John Magufuli a "dictator," party sources said.
No reasons were given for the arrest of Lissu, a member of the main opposition Chadema party, who serves as the chief whip of the opposition in parliament and also leads Tanzania's Bar Association.
Lissu was arrested on Thursday at Dar es Salaam airport as he attempted to take a plane to Rwanda, Chadema spokesman Tumaini Makene said.
On Sunday, Magufuli warned opposition leaders against "reckless" remarks and ordered authorities to take action against any opposition leader who incites violence.
In response to his comments Lussi told reporters on Monday that repeated arrests of senior party members, locally and nationally, were intended to muzzle any opposition to Magufuli, adding that "the dictator and his government, to be isolated politically, diplomatically and economically."
Magufuli, whose nickname "tingatinga" means "bulldozer" in Swahili, swept to power in 2015, presenting himself as a no-nonsense, corruption-busting, man-of-the-people.
However, the opposition has accused Magufuli for his blunt leadership style, of presiding over an increasingly authoritarian government.
Over the past few months, more than 10 people, including university students and a lecturer, have been charged in court with insulting the president via social networking platform like WhatsApp.
In Junei Tanzanian authorities banned a newspaper for two years over articles it published linking two former presidents to alleged improprieties in mining deals signed in the 1990s and early 2000s.