The United States international's positioning was criticised for Bournemouth's last-gasp equaliser in Saturday's 3-3 draw.
It is not the first time the 36-year-old has come under scrutiny this season but Martinez has defended the American - although he will not play in Tuesday's Capital One Cup quarter-final at Middlesbrough as Spaniard Joel Robles will start, as he has done in previous rounds.
"Joel was man of the match in the previous round and he will start tomorrow - that is something which has been planned," said the Everton manager.
"Since Tim came back into the side after the previous round he has been very consistent, performing with a real influence over the back four.
"The third goal was a real disappointment because it was the last kick of the game but as a team we should have done a lot better, not relying on the goalkeeper.
"When someone has a free header in the six-yard box there has to be questions over the marking."
Joel has made just three appearances - all in this season's Capital One Cup - since February but Martinez maintains the 25-year-old is Howard's equal.
"Gone are the days when you have only one goalkeeper and then you are waiting for him to get injured or suspended," he added.
"You have to have two very good number ones who both can play different roles: Tim Howard is an incredible source of experience and someone who can give direction to young players.
"Joel has the potential to be a very special goalkeeper and that is why we brought him to the club.
"It has been important for him to be playing in the League Cup
He has shown a good level, especially against Norwich where his mentality more than anything else was tested in a penalty shoot-out.
"We need a squad which has two very strong goalkeepers and that is the case."
Defender Leighton Baines is set to make his first appearance of the season in the matchday squad having been sidelined since May 9 after ankle surgery.
However, midfielders James McCarthy and Gareth Barry look set to be rested after sustaining injuries at the weekend.
"Leighton trained really well yesterday
He is medically fit now, it is just making sure we get the right feeling and he feels confident and the match intensity he gets in training helps him," Martinez added.
"His experience could be important tomorrow
We will assess him and see if he can be involved - that doesn't mean he has to play from the start but it would be a good sign to have him involved in the squad."
On McCarthy Martinez said: "We will have a clearer picture today.
"He had to come off in the game after he over-extended his upper hip muscle and yesterday he was quite sore.
"Gareth Barry had a really nasty knock in the shin - there are stud marks - and he was finding it difficult to walk yesterday."
Everton are in the quarter-finals of the League Cup for the first time since 2008 and while they are unbeaten in five matches and ninth in the Premier League, Martinez does not believe they have any additional advantage over their opponents, who are second in the Championship and have lost once in seven games.
"In this competition I don't think divisional status gives you a benefit," said the Toffees boss.
"You need to be ready for the game with a clear understanding of how to perform.
"Clearly the mentality in our camp is to be ready - we can't not be ready after the feeling at the weekend."
Source : PA
Source: PA