Kenyan politician, lawyer for Tanzania opposition leader arrested
Karua has been representing Tanzanian opposition leader Tindu Lissu, who is on trial for treason and faces a possible death penalty.
Lissu is due in court on Monday.
The trial comes as Tanzania prepares for elections in October.
Karua "was detained at Julius Nyerere International Airport in Dar es Salaam, questioned for three hours, her passport was confiscated and she is awaiting deportation", the spokesperson said.
A former justice minister in Kenya, Karua has been vocal about "democratic backsliding" in the East Africa region.