"We are a little bit surprised about the quantity of points we have and a bit surprised about the weekend result," Alonso told reporters.
The Spaniard is level on 61 points with Vettel, while Briton Lewis Hamilton is third on 53.
Formula One fans are enjoying the most topsy-turvy season for years, with five different drivers having won the first five races, the first time that has happened since 1983.
Alonso said he was hoping for some improvements from his car after testing in Italy in recent weeks but that the second place was perhaps misleading.
"I think maybe we outperformed a little bit in terms of the potential we have and maybe some other teams underperformed or had some problems."
Alonso won against the odds in a wet Malaysia in March but made it clear that Ferrari, the most famous team in Formula One, had more work to do to be consistently competitive.
His team mate Felippe Massa of Brazil has picked up only two points all season.
"We have had the most difficult start in the championship in my three years at Ferrari with a car that was not competitive at all," he said.
"When we are first and second in qualifying and first and second in a race, then we can say we have the best car."