The suspects, mostly young men who "received training in Pakistan", were seized and disarmed in the capital of Dushanbe, a representative of the Tajikistan interior ministry told AFP.
"They were preparing a series of blasts on government facilities in four districts of Dushanbe... A hostage siege, and subsequently the presentation of ultimatums to the authorities during the presidential elections," the official said.
The suspected militants are Tajik nationals and have received training in Waziristan, a region bordering Afghanistan known as a stronghold of Islamists linked to the Taliban and Al-Qaeda.
President Emomali Rakhmon, who has headed the country since 1992, last month called presidential elections for November. He is widely expected to win.
Tajikistan, where a bloody civil war between Islamist forces and Rakhmon backers followed the collapse of the Soviet Union, shares a porous 1,300-kilometre border with Afghanistan.
The impoverished former Soviet republic has previously accused religious groups of stoking unrest in a bid to impose Islamic rule.