Bulgaria's Interior Ministry announced on Saturday that 38 men, 33 women and 58 children were found hiding among goods on the truck at the border crossing of Kapitan-Andreevo.
The ministry spokeswoman said most of the asylum seekers were believed to be Syrians, adding that the truck driver had taken into police custody.
The failed attempt to cross the border into the European Union in a refrigerated truck is reminiscent of a similar case in August when 71 migrants were found to have frozen to death in a cold-storage truck designed to carry frozen food.
Bulgarian police on Saturday made checks of some 6,000 vehicles and arrested 16 suspected traffickers as well as 495 refugees nationwide seeking to transit the country clandestinely.
Authorities fear increased arrivals ahead of the cold winter season.
According to the International Organization for Migration (IOM), over 680,000 refugees fleeing from war, insecurity and persecution in the Middle East and North Africa have landed on European shores this year after making perilous sea journeys from Turkey to Greece and across the Mediterranean Sea to Italy.
More than 3,000 have died or gone missing trying to reach Europe.