The Cobblers beat Championship side Reading to secure a place in the third round that takes them to Anfield on Wednesday evening.
Thornton told BBC Radio Northampton: "You always dream of playing in the Premier League, against those players. We're not expected to beat them so we've got to enjoy it. If we get the ball down and play, we're a good team."
Thornton joined Northampton Town from Nuneaton Borough in January having previously played for Coventry City and Brighton.
He has scored in the cup tie with Reading, and in League Two against Shrewsbury and Wycombe Wanderers.
"The manager wants me to play higher up the field, as that's where he thinks I'm dangerous," he said.
"I'm just concentrating on staying in the team, and trying to do well for myself and the team."
Source: BBC Sport
Source: BBC Sport