The league released a statement about the fine handed down, but Smart avoided a potential suspension.
The NBA said Smart was fined for "aggressively pursuing an opponent in an attempt to escalate a physical altercation and failing to leave the court in a timely manner following his ejection."
The Celtics defeated the Hawks 113-105 on Saturday night. Midway through the third quarter of the contest, Smart picked up his second technical foul after arguing with Bembry before a jump ball.
The second technical foul automatically led to Smart's ejection, but the fiery guard refused to leave the court immediately. Multiple players and officials restrained Smart until he broke free and charged at Bembry. The Celtics guard eventually took off his jersey and walked toward the tunnel.
Smart picked up his first technical foul earlier in the game after arguing calls with referees.
The Celtics (28-18) play the Miami Heat (22-22) on Monday night at TD Garden.