The 230,000 members of the Central Asian country's security forces were alerted for the test at 4am on the order of President Emomali Rakhmon.
Dushanbe also relocated 20,000 troops to strengthen its force on the border with Afghanistan.
The military inspection was the first of its kind in the ex-Soviet country's 30-year history.
The operation was broadcast on Tajik state television and ended with a military parade headed by Rakhmon in which he called on Tajiks to be "ready to defend peace and stability" in the region.
"The situation in our neighbouring country -- the Islamic Republic of Afghanistan, especially in its northern regions that border our country, remains extremely complex and uncertain," Rakhmon said.
"It is getting more complicated day by day and even hour by hour," he said.
He called on the armed forces and law enforcement agencies to "ensure the highest level of combat readiness to prevent potential threats" and to "ensure the protection of the state border".
Rakhmon, who has led Tajikistan since 1994, then spoke to his Russian ally, President Vladimir Putin.
The Kremlin said the pair discussed the situation in Afghanistan and that the phone call took place "on the initiative of the Tajik side".
The Taliban's offensive has seen a stream of Afghans make their way across the Tajik border.
The Taliban in recent weeks have brought huge swathes of Afghanistan under their control as foreign troops draw down, including the main Shir Khan Bandar border crossing with Tajikistan.
"Afghanistan's borders with Tajikistan, Uzbekistan, Turkmenistan, and Iran, or about 90 per cent of the border, are under our control," Taliban spokesman Zabihullah Mujahid told the Russian RIA Novosti news agency, a claim that could not be independently verified.