The Blues hold a four-point lead over Liverpool and Arsenal, but Manuel Pellegrini's men, two points further back, have the chance to take the top spot on goal difference should they win their additional matches.
"I'm not top of the league, that's the problem," Mourinho told reporters. "I'm only really top of the league the day my team have played the same number of matches as the other teams, and I have more points.
"If that happens, I can say I'm top of the league. Until that moment, if other teams have matches in hand and can be top of the league if they win them, they are top of the league.
"So at this moment I'm not top of the league."
With Manchester City in FA Cup action against Wigan on Sunday, Chelsea has the chance to extend its lead at the top even further against Tottenham at Stamford Bridge on Saturday.