She told reporters that she was a "perfectionist" and - due to lack of rehearsal time - "did not feel comfortable taking a risk".
"I wanted to make him [Obama] and my country proud, so I decided to sing along with my pre-recorded track."
"I'm very proud of my performance," she said.
The star opened the press conference in New Orleans by asking reporters to stand before performing a live rendition of the national anthem.
Highlight
Millions of people tuned in to watch President Barack Obama sworn in for his second term in office on 21 January, which included performances by James Taylor, Kelly Clarkson and Beyonce.
The pop star's performance of the Star Spangled Banner at the inauguration was considered one of the highlights of the ceremony, but later reports suggested the singer had recorded her vocal.
"I am a perfectionist and one thing about me is that I practise until my feet bleed and I did not have time to rehearse with the orchestra," the Grammy-winning artist said on Thursday.
She said her decision to mime the track was triggered by the weather, delays and "no proper soundcheck", adding that pre-recording is "very common in the music industry".
"It was a live television show and a very, very important emotional show for me and one of my proudest moments," she said.
However, she insisted she would be singing live for her half-time Superbowl performance on Sunday - one of the most-watched TV events in the United States.
"I will absolutely be singing live. This is what I was born to do, it is what I was born for."
The National Football League also announced that singer Jennifer Hudson would be performing America the Beautiful with the chorus from Connecticut's Sandy Hook Elementary School, where 20 children and six adults were killed in a mass shooting in December.
Last year's Super Bowl half-time show, performed by Madonna, was watched by an average of 114 million viewers, while Janet Jackson's notorious 'wardrobe malfunction' - in 2004 - generated a record number of complaints for broadcaster CBS.
Singer Beyonce has admitted miming during her rendition of the American national anthem at the inauguration of President Obama last month.