The Red Devils recorded their eighth straight top-flight victory on Sunday as they overcame West Ham United to climb back to the top of the table.
United currently lead second-placed Liverpool by two points, boasting a game in hand, but Ferguson has warned his charges that they must maintain their focus.
"Mistakes can be made. We had an 11-point lead over Arsenal in 1998 and lost the league, so we are not counting our chickens," he said.
Record breakers"We shouldn't either because this game can come and bite you. This is a fantastic result and performance. It is time to kick on."
United defeated West Ham 1-0 to secure a 13th consecutive clean sheet as goalkeeper Edwin Van der Sar set a British league record for the longest run without conceding a goal.
Of the feat, Ferguson said: "For Manchester United, over 20 hours without conceding a goal is extraordinary because normally we get scorelines like 4-3.
"It is great credit to the players. I am very proud of them."