The Bantams are unbeaten having taken 10 points from the first four fixtures, but the West Ham loanee is expecting another tough game against Oldham Athletic at Valley Parade.
He said: “The confidence is high, but at the end of the day it’s only three wins. We’ve got to stay focused and take every game as it comes.
“We’re bouncing off one another at the moment, but every game is tough in League One so we’ve got to be right at it.
“With the way we have started, teams will be looking at us, so they’ll come and put in a good performance. We expect a tough game, but we’re quietly confident of getting a result.”
Cullen spent last season at Valley Parade and while he is familiar with a number of players, he has praised the new additions.
“The new faces have boosted the squad,” he said. “The quality is high and when you’ve got good players around you, you can trust them straight away.”
One of those new players is fellow midfielder Timothee Dieng, a summer signing from Oldham. The Frenchman has been restricted to two substitute appearances after suffering a calf injury, but has declared himself fit to face his former employers.
“I’ve trained the last two weeks and I’m fit to play 90 minutes. Stuart McCall picks the team but I’m raring to go,” he said.
“I spent two years at Oldham and it was a very good time. I really enjoyed it so it would be great to play against some familiar faces.
“It’s similar at Bradford. We have good team spirit, a good squad and amazing fans. It will be a nice day personally.”