Terry, making his first start since the EFL Cup exit at West Ham in October and first appearance since November, was adjudged to be last man when he fouled Lee Angol and was shown a straight red card by Friend.
Conte felt Terry did not make contact with Angol and Branislav Ivanovic was a covering defender.
"I think it wasn't right, this decision from the referee," Conte said.
"He didn't take the opponent and also the second reason was because behind John there was Ivanovic to cover John.
"You have to respect the referee decision, but in this case maybe we will do an appeal for this situation.
"The situation is very clear and I think John didn't deserve this.
"It's a pity when this happens, because the red card is not good."
Terry's time at Stamford Bridge could be nearing an end
He was 36 last month and his contract expires in the summer.
In January 2016 Terry disclosed that he had not been offered a new deal and that he would be leaving that summer.
But he was later offered and then, after a period of deliberation, signed a 12-month extension last May, concluding an issue which had shrouded the second half of last season for the Blues.
Conte insisted the decision on the future of Terry, who made his first-team debut more than 18 years ago, would be made with the club and was adamant he was happy with the club captain.
"I'm pleased for John, because he's showing me great commitment when I ask him to play, when he doesn't play," Conte added.
"He's helping me a lot in the changing room
He's showing me to be a good player, but above all a good man."
Conte on Sunday recalled Nathan Ake from his loan spell at Bournemouth
The Dutchman provides additional competition for Terry as he can play in central defence or potentially as a left wing back.
"Ake gives me important options," Conte said.
"Chelsea is his home
He's showing he deserves to stay in a great team like Chelsea."
Conte remained coy on transfers, with the winter window open, and declined to address speculation of a move for Swansea's Fernando Llorente, with Michy Batshuayi reportedly going in the opposite direction temporarily.
Batshuayi scored his first goal since August as Chelsea took a 3-0 lead prior to Terry's dismissal, netting between strikes from Pedro and Willian.
The £33million summer signing from Marseille appeared anxious to impress and might have scored more.
Of Belgium striker Batshuayi, Conte said: "Michy played a good game.
"He showed me great commitment, great workrate
Also he scored a goal
For a forward it's always important to score for confidence.
"Now it's important for him to continue in this way and to give me the opportunity to have another solution in our squad."
Conte made nine changes to the team which began last Wednesday's defeat at Tottenham, which saw the Blues' 13-game winning run in the league come to a halt.
He was pleased with the return of Kurt Zouma, in particular.
"When you change nine players it's not easy to find quickly your idea of football
Instead it happened," Conte added.
League One Peterborough attacked Chelsea from the start, but that led to openings for the hosts which they exploited.
The visitors claimed a consolation when Tom Nichols pulled a goal back, but Pedro struck his second to complete victory.
Peterborough boss Grant McCann said: "The difference in the game was they were clinical, we weren't.
"I don't think we came here and disgraced ourselves
We could've come here and defended deeper and tried to frustrate them.
"But I thought we may as well come here and give it a go
I thought we did that.
"The fourth goal just knocked the stuffing out of us
It just killed the momentum for us
We were just seeing the rest of the game out."
Source : PA
Source: PA