Egypt international Salah scooped a host of individual awards, including the golden boot, last season after netting 44 goals in all competitions for the Reds.
Aguero however is the second highest scoring overseas player in Premier League history and last month entered the top 10 in the all-time standings after goals against Cardiff City and Brighton and Hove Albion - surpassing Teddy Sheringham.
"He (Salah) is younger and it was his first year back in England since his time at Chelsea, so we will see in the future," said Guardiola.
"But a guy who has the quality to score 50 goals in a season always has that quality. But football is all about ups and downs.
"Salah remains an excellent player and will score goals in the future. When you are in there scenting goals sometimes this happens.
"Sergio has scored a lot of goals but there were periods when he didn't score goals.
"How many years has Sergio scored all those goals, eight or nine years? For Salah it was the first one so we will see in seven or eight years."
Salah is yet to recapture his form from his maiden campaign at Anfield, scoring just three times in 10 appearances this season and was even taken off during the 1-1 draw with Chelsea last weekend.
The ex-Roma winger scored in two of Liverpool's three wins over Man City last term and they will hope to make it five home league wins in a row over Guardiola's men when the two sides meet on Sunday.
Guardiola has not been surprised by Liverpool's impressive start to the season - they have won six and drawn one of their seven league games just like City - but has refused to name them as the only challengers for the Premier League title.
"But for us, for Manchester City, we want to defend our title, and they are contenders. Liverpool have started so well, they have the same points us, but we were expecting that all along.
"Liverpool were an excellent team last season and since then they have bought some more incredible players to fight against us."