The woman was receiving threatening messages from a Facebook profile since last month, police said.
B Hemanth Kumar, the accused, said in the messages that he had some obscene videos of her, and he would upload them on porn websites if she didn't grant him sexual favours, police said.
After the woman lodged a complaint, investigation revealed that Kumar, who was her classmate in high school, was the creator of the fake profile and was trying to blackmail her, police said in a statement.