Silva is reported to be interested in quitting the Premier League champions for personal reasons.
The 28-year-old was on the bench for City's first two games this term before starting and scoring in Sunday's 3-3 draw at Newcastle.
Barcelona and Paris Saint-Germain have both been linked with Silva in recent weeks.
Guardiola was asked about Silva's future following City's midweek friendly against Barcelona and appeared to suggest he could leave if an acceptable offer was made.
But the Spaniard is now adamant Silva will still be at the Etihad Stadium after the window closes on September 1.
"He's staying here, absolutely. We don't have any phone call from any club regarding Bernardo Silva, so he will stay," Guardiola told reporters on Friday.
"I am telling you, he will stay."
Raheem Sterling, Gabriel Jesus and Oleksandr Zinchenko were among several high-profile departures from City after last season's title triumph.
Erling Haaland and Kalvin Phillips have come in to freshen up the champions and Guardiola insisted he is happy with his squad.
"I am always satisfied. For six years, now starting a seventh, I am always satisfied with the squad I have," he said.
However, City will go into Saturday's Premier League game against Crystal Palace short of defensive options because of injuries to Aymeric Laporte and Nathan Ake.
Teenager Luke Mbete replaced Ruben Dias against Barcelona on Wednesday but was then forced off after a clash of heads with Andreas Christensen.
"We train this afternoon and we will know exactly the situation with everyone. Now I cannot tell you," Guardiola said of City's mounting injury list.