George Obama in jail
Inspector Augustine Mutembei, the officer in charge, said Obama was arrested on charges of possession of cannabis, known in Kenya as Bhang, and resisting arrest. He is scheduled to appear in court Monday, Mutembei said.
He is being held at Huruma police post in the capital of Nairobi.
Correspondent David McKenzie talked with George Obama at the jail where he is being held. Speaking from behind bars, Obama denied the allegations.
"They took me from my home," he said, "I don't know why they are charging me."
George Obama and the president barely know each other, though they have met before. George Obama was one of the president's few close relatives who did not go to the inauguration in Washington last week.
In his memoir, "Dreams from My Father," Barack Obama describes meeting George as a "painful affair." Barack Obama's trip to Kenya meant meeting family he had never known.
McKenzie tracked down George Obama in August 2008 and found him at a small house in Huruma, a Nairobi slum, where he lives with his mother's extended family. His birth certificate shows he is Barack Obama's half brother.
The two men share the same Kenyan father. In the memoir, Barack Obama struggles to reconcile with his father after he left him and his mother when he was just a child.
Barack Obama Sr. died in a car accident when George was just 6 months old. Like his half brother, George hardly knew his father.
George was his father's last child and had not been aware of his famous half brother until he rose to prominence in the Democratic primaries last year.
Unlike his grandmother in Kogela, in western Kenya, George Obama had received little attention from the media until reports about him surfaced in August 2008.
The reports sprung from an Italian Vanity Fair article saying George Obama lived in a shack and was "earning less than a dollar a day." Those reports left George Obama angry.
"I was brought up well. I live well even now," he said. "The magazines, they have exaggerated everything.
"I think I kind of like it here. There are some challenges, but maybe it is just like where you come from, there are the same challenges," Obama said.
Obama, who is in his mid-20s, said at the time that he was learning to become a mechanic and was active in youth groups in Huruma. He said he tried to help the community as much as he can.
I guess it's a family business