Third-place City visit second-place Liverpool on Saturday (17:30 GMT) as they look to close the gap on leaders Chelsea, who are six points clear.
Such is the size of the advantage that Arsenal boss Arsene Wenger says it is "Chelsea's title to lose".
But Guardiola said: "Six teams are fighting for the title and the Champions League qualification."
The Reds have won their last three league games against City, who have not won at Anfield since 2003 - a run of 14 Premier League and cup games.
The two sides are separated by just a single point, but they could find themselves even further behind the Blues, who host Stoke earlier on Saturday (15:00 GMT).
Former Barcelona boss Guardiola added: "Liverpool are a contender. The contenders are really tough. It will be a good fight until the end of the season. Anfield will be a big role for them. We have to match their intensity."
The Spaniard also confirmed striker Sergio Aguero is "ready" to return after serving a four-game domestic suspension.
...but Chelsea are making it look just that at the moment.
Victory over Bournemouth in their last league game stretched Antonio Conte's side's winning run to 12 games - a club record - and they last dropped points in September against Arsenal.
Italian manager Conte said: "We have only played 18 games. Another 20 to finish the season. At the start of the season no-one trusted in this team to fight for the title. We have only six points more than the second team. There is still a long way to go. I am pleased with the players.
"I think the most important thing in our head is to continue to work very hard and be focussed game by game. This league is not easy. Twelve wins in a row is a great achievement but it is not enough to win the league. I want to keep this run going."
Arsenal had momentarily taken top spot early in December after beating Stoke, albeit having played a game more than Chelsea, but back-to-back defeats against Everton and title rivals City has seen them slip nine points off the pace.
Frenchman Wenger said: "Chelsea is the super favourite. They have a big difference, it is theirs to lose. At the moment they have won it but they can still lose it. The head to head games are of vital importance."
Manchester City manager Pep Guardiola feels there are still six clubs in the Premier League title race.