Barca, who won the Champions League last season and the La Liga title losing only twice in 38 matches, have been acclaimed as the best club side ever. They go into Friday's Super Cup final against Porto seeking their 12th trophy since 2007.
While Porto coach Vitor Pereira described Barca "as the best team I have seen in my lifetime" before trying to stop Barca at the Stade Louis II, Guardiola said his team could easily be beaten.
"First of all we are not unbeatable. Each team can beat us. We receive a lot of compliments because we have won 11 prizes in the last four seasons," he said.
"But the more successful you are the harder it becomes and the harder your opponents want to beat you.
"We have to try and forget the past. The most important match is the next one so let's try to focus and keep going and for the players to show to the world they still have desire."
Trying to keep in perspective where his team stands in the pantheon of Barca teams of the past, he also said they had not yet proved themselves as the best Barcelona team ever.
"I have always had ridiculously good teams. We forget that the former team won three titles, and the team before that won six titles, so to say this squad is better than other squads cannot be said. This current squad needs to prove it on the pitch.
"It will be decided by history. We try to do the best we can afterwards people will be able to judge whether they like it or not," Guardiola said.
IMPECCABLE STATISTICS
He was also full of praise for Porto who won the Europa League last season and the Portuguese title without losing a game.
Porto have sold some key players since last season's triumphs, and Guardiola said: "They are being sold for 25 to 30 million euros because they can make it. Everyone in Europe would like to have these players, they are a really strong side in every way.
"They won the league without losing a match - look at their statistics, they are impeccable.
"Otamendi, Orlando, Moutinho, the two wingers, Hulk, all the players are extremely valuable and can play in any major European team, but they are already playing in a very big European team in Porto."
The mutual apprecciation did not end there with Porto coach Pereira, who took over when Andre Vilas-Boas left for Chelsea at the end of last season, describing Barca as the best side he had ever seen.
"However, we are not coming here just to watch Barca play. We are here on merit after winning the Europa League last season and we are here to win the Super Cup.
"Of course Barca are difficult to beat, but I believe in the players I have and the game plan I have worked out which hopefully will see us win the game."
He also denied reports in England that Chelsea had made a bid for Uruguayan defender Alvaro Pereira, who is not expected to play against Barca.
"As far as I am aware there has been no contact from Chelsea for any of our players," he said.
