Evan Mawarire, who left the country last year in fear for his life, was arrested at Harare International Airport.
The BBC's Shingai Nyoka reports that police have not said what he has been charged with.
The pastor backed a stay-at-home strike last July, which was one of the largest anti-government protests in years.
Mr Mawarire first came to fame last April when he posted a video on Facebook of himself wrapped in a Zimbabwean flag complaining about the state of the nation.
It sparked a #ThisFlag protest movement against the leadership of the country.
Protesters were demanding that civil servants were paid on time, roadblocks were reduced and police officers stopped harassing people for cash.
They also demanded that President Robert Mugabe fire and prosecute corrupt officials.
In July, protesters staged a national "shutdown" which led to a complete closure of schools, businesses and shops across the country. It was the biggest strike action since 2005.
Mr Mawarire was arrested and charged with inciting public violence but a court ruled police had violated his rights and released him.
He left the country soon after.
He has been in the US for about six months.
When he landed in Zimbabwe on Wednesday, Mr Mawarire "was escorted into another room by three men even before he went through immigration or customs", his sister Telda Mawarire told AFP news agency.
Our correspondent reports that, after being detained at the airport, Mr Mawarire was taken to a police station in the centre of the capital, Harare.
A Zimbabwean pastor who criticised his government has been detained after flying back to the country.