Fire crews from five stations tackled the blaze at Bella Roma Italian on Northgate at 2.25am on Saturday.
The fire started in a back room on the first floor and spread to the roof.
It is not thought to have been malicious and caused only minimal damage to the kitchen and restaurant areas.
Proprietor Felice Di Giorno, who took over the business six years ago, said: “All being well we will be ready to open again in a couple of weeks.
“Part of the roof came down and we are rebuilding it now.
“Luckily there was no damage to the restaurant, apart from a bit of water on the floor and the kitchen is okay.
“The workmen are coming in this week to make it watertight, so fingers crossed we should be up and running again in the next two to three weeks.
“A lot of the work is just precautionary, we’re lucky that there was no further damage.”
Fire crews from Wakefield, Ossett, Normanton and Dewsbury were all involved in the response and an aerial appliance was dispatched from Leeds.
When the alarm was raised in the early hours of Saturday morning it was initially feared that people might have been trapped inside.
However, they found nobody at the site..
A fire service spokesman said they brought the fire under control using three hose reels and breathing apparatus.
He added that a fire investigation officer had been due to attend the scene to establish the cause of the fire.
Fire investigation officer, watch manager Ian Firth, said: “The fire was accidental, however investigations are ongoing at the moment due to the extent of damage in area where the fire started.
“The building was secure on arrival, fire was through the roof and 50 per cent of first floor involved. Entry was forced through two doors.”