Brian Doyle, 55, faces 23 charges in Polk County, Florida, related to the use of a computer to seduce a child and transmitting harmful material to a minor, Polk County Sheriff Grady Judd said in a statement.
Mr Doyle was allegedly taken into custody at his home in Silver Spring, Maryland, outside Washington, while he was communicating with what he believed was a 14 year old, Mr Judd said.
"He was on his computer communicating with the undercover detective who he believed to be a 14-year-old girl at the time we knocked on his door in Maryland, took him into custody and served a search warrant," Mr Judd told CNN.
The police statement said Mr Doyle contacted the 14 year old girl on March 12, from a profile posted on the Internet and initiated a sexually explicit conversation – it was a conversation that also revealed his role in the US Department of Homeland Security.
The "girl" was actually an undercover Polk County detective.
In subsequent conversations, Mr Doyle gave the “girl” both his office phone number and his government-issued cell phone number.
The statement alleges that Mr Doyle used the Internet to send pornographic movie clips to the "girl" and had explicit sexual conversations in online chats with "her."
The police statement also alleges that Mr Doyle also had sexually explicit telephone conversations with a detective posing as a child on his office telephone and cell phone.
"There is no question that Doyle believed that he was having these disgusting, obscene discussions, on-line and on the phone, with a young girl," Mr Judd said.
Security risk
"What stands out to me the most in this particular case was the fact that Brian, on his first conversation with our undercover detective, who he believed to be a 14-year-old girl, clearly identified himself as a deputy press secretary for Homeland
Security," Mr Judd told CNN.
"If he would provide that kind of information to include a photograph of himself with his identification tags, who else may he be talking to around the world who he thinks to be a 14-year-old girl?"
The sheriff added that Mr Doyle could face more charges from a federal investigation now underway.
A Homeland Security official said Mr Doyle was expected to be put on administrative leave.