The France striker struggled to live up to his 35 million euro price tag after joining from Olympique Lyon in 2009 but has looked close to his best in the last month.
A double in the 2-0 win over Hercules in La Liga on Saturday made it eight goals in his last six outings, taking his tally for the season to 19 in all competitions.
"I like to have selection problems and to have to choose, and that nobody has a guaranteed place," Mourinho told reporters at the Bernabeu after Saturday's victory.
"Karim is doing better than ever and is doing things he never did before. We joke that now he is even winning headers at the near post on corners we are defending. He's happy.
"With Cristiano Ronaldo and Gonzalo Higuain out injured he has scored four goals in the last two games to secure six important points (in the league)."
Benzema has started the last two matches up front with Emmanuel Adebayor, who was brought in on loan from Manchester City in January as the 23-year-old struggled to find his range.
Mourinho has tinkered with his formation to incorporate the two strikers but is likely to revert to one again when Ronaldo makes his expected return from a calf strain against Lyon in the champions League on Wednesday.
Real are trying to reach the quarter-finals for the first time in seven years and need to build on a 1-1 first leg draw.
Adebayor started up front in Lyon last month but it was Benzema who came off the bench to net the equaliser and he may have done just enough to win a place in the starting line-up against his former club this time round.
