Peter Sawali was charged this week with conduct likely to cause breach of peace, said police spokesman Davie Chingwalu.
Sawali, 21, was putting up posters that read, "Gay rights are human rights," on a busy road in the city of Blantyre, the spokesman said.
The man had stacks of glossy posters with the same message in his possession, according to the spokesman. An investigation is under way to seek more suspects, because Sawali said he was not acting alone.
"Homosexuality is illegal in Malawi and is punishable by prison time and hard labor," Chingwalu said. "Basically, he was promoting a criminal act. This is what this is all about."
If convicted, Sawali would face up to five months in prison, hard labor and a fine of about 2,000 kwacha ($14), police said.
Homosexuality is a largely taboo subject in Malawi.
In late December, Steven Monjeza, 26, and Tiwonge Chimbalanga, 20, were arrested and charged with public indecency after they became engaged in the country.
The two pleaded not guilty and were detained pending trial. They are thought to be the first openly gay couple to pursue a public marriage in Malawi, according to the spokesman.
An investigation also is under way to determine whether Sawali is linked to the couple.
The arrests have sparked international outcry from human rights organizations. Last month, Human Rights Watch wrote a letter to Malawi's government, accusing it of threatening citizens' fundamental rights.
"Prosecuting two adults just because they affirm their love is a terrible injustice," said Dipika Nath, of the lesbian, gay, bisexual and transgender rights program at the New York-based organization.
The country is abiding by its constitution, the spokesman said.
"All these countries want to impose their culture on us, but homosexuality is a crime, according to the penal code in Malawi," he said. Those found guilty of homosexuality in Malawi face a maximum of 14 years in jail.