The Turin giants looked on course for their 20th victory in Verona after Carlos Tevez had given Juve a 2-0 lead after 21 minutes.
But Hellas battled back and substitute Juanito popped up in the 90th minute to earn his side a 2-2 draw.
"It's inexplicable," Conte said to Gazzetta dello Sport."We threw away all the good work we had done.
"We were punished by two set plays on two defensive distractions and that is unacceptable."
Conte felt his side should have killed the game off in the opening half.
"We could have done a lot better," he said. "I am perplexed that we dominated the opening half only to end up with a point.
"We have to be more focused because it is a question of concentration.
"It's a shame we drew this game against a Verona side that created few opportunities.
"I have to compliment them for their determination."
A win on Sunday would have seen Juve go 11 points clear of second-place Roma, who were held to a goalless result at Lazio at the weekend.
Roma have a game in hand while Juve host Chievo on Sunday.