The agency has registered a case against Roy, his wife Radhika and RRPR Holdings for allegedly causing losses of Rs 48 crore to ICICI Bank, CBI sources said.
They said the agency was conducting searches at four places in the national capital and Dehradun.
"This morning, the CBI stepped up the concerted harassment of NDTV and its promoters based on the same old endless false accusations," NDTV said in a statement.
"We will not succumb to these attempts to blatantly undermine democracy and free speech in India. We have one message to those who are trying to destroy the institutions of India and everything it stands for: we will fight for our country and overcome these forces," it said.