The actress landed at the airport at around 2am from Bangkok by a Thai Airways flight.
"She was passing through the green channel (used by passengers not having any dutiable goods to declare) when she was stopped and asked to show her baggage," he said.
During checking, the actor was found carrying undeclared items like branded purses and cosmetics worth Rs2 lakh. This amounted to duty evasion, the official added.
Mirza was asked to pay a fine of over Rs1 lakh. She was allowed to go after she paid the amount, he said.
The 30-year-old model-turned-actress claimed she was not aware of Customs rules about dutiable goods and did not intend to evade duty, the official added.
Mirza is the latest film personality to land in trouble over declaration of dutiable goods. Last year Bipasha Basu and Minissha Lamba, among other film and television personalties, were detained at the airport after they were found carrying undeclared goods.