Mr Brazeau, who was already suspended from the senate, and Mr Harb, who resigned in August, were also charged with breach of trust.
They, along with two other senators, were the focus of outside audits of their expenses last year.
The two men deny the charges.
Authorities say the senators claimed reimbursement for travel and housing expenses for secondary residences near the national capital, Ottawa, even as they in fact lived there full-time.
"Canadians expect the RCMP to be exhaustive and unbiased in our investigations," Gilles Michaud, the RCMP's assistant commissioner, said in a statement on Tuesday. "These investigations were detailed and involved careful consideration and examination of evidence."
Mr Harb, a Liberal Party senator from Ontario and former MP, left the Senate in August 2013, dropping his challenge against an order that he repay 231,000 Canadian dollars ($220,000; Â£141,000) for improperly claimed expenses.
The remaining three, Mr Brazeau, Mike Duffy, and Pamela Wallin, all Conservatives, have been ordered to pay back thousands in expenses and were suspended from the chamber by a vote in November.
Mr Harb and Mr Brazeau, who represents the Repentigny, Quebec, division, were the only two charged on Tuesday. It is unclear if RCMP officials will bring charges against Mr Duffy, representing Cavendish, Prince Edward Island, or Ms Wallin, representing Saskatchewan, in the future, but Mr Michaud said the RCMP was continuing its investigation.
Mr Harb's lawyer, Sean May, told broadcaster CBC it was "disappointing that charges are being laid. He's going to be prepared to respond in court and he looks forward to that."
Mr Brazeau has previously said he will fight any charges.
Canadian senators are appointed by the governor general of Canada - the Queen's representative - on the advice of the prime minister. They typically join either the government caucus or the opposition caucus, or sit as independents.

The 20-year-old's four-month loan with the League One Shrews ends in January.
"Why change the environment? Why does he need to go and play in the Championship?" Pardew told BBC Sport.
"I'd be quite happy for him to stay where he is - the manager's done a super job with him."
Kaikai has netted five times in 12 league games for Town so far and it is the competitive nature of life in League One that Pardew wants the player to carry on experiencing.
"He's liked playing for the Under-21s, but there's no league table and at that level (at Shrewsbury) it's life and death," he said.
"For Sullay to deliver there is great news for us  - I'm very pleased and if I don't call him back, hopefully he can stay there."

Greater Manchester Police said the corrosive liquid hit a man and a woman in the eyes on Ashton Old Road, Openshaw, Manchester on Friday evening.
Shortly afterwards, bleach was thrown at a second man on the same road by a passenger in a silver Ford Fiesta heading towards Audenshaw.
Police said those affected were "lucky" to escape serious injury.
Insp Cherie Dunn, of Greater Manchester Police, said: "I am so thankful that none of the victims of these senseless attacks has been seriously injured.
"We could easily have been dealing with life-changing injuries.
"Anyone thinking that throwing bleach at people is funny or that a crime like this does not have consequences couldn't be more wrong.
"The victim's here were lucky. Bleach attacks could have had catastrophic consequences."
The Royal Canadian Mounted Police (RCMP) have charged Senator Patrick Brazeau and ex-Senator Mac Harb with fraud, saying they claimed improper living and travel expenses.
[NEXT_CONCEPT]
Shrewsbury Town manager Micky Mellon is doing a "super job" with striker Sullay Kaikai and he is better off there than at a Championship club, says Crystal Palace boss Alan Pardew.
[NEXT_CONCEPT]
A pregnant woman was among three people targeted when bleach was thrown from a car in two separate attacks.