The report said they were from the Strong Armenia party, led by Russian-Armenian billionaire Samvel Karapetyan, who is under house arrest on charges of calling for the overthrow of the government - accusations he rejects as politically motivated.
Armenia's relationship with traditional patron Russia has emerged as a central electoral issue.
Russia has slapped restrictions on Armenian exports in recent weeks in response to the country's warming relationship with European countries.
About 2.4 million Armenians will be eligible to cast their ballots in Sunday's election, which is also seen as a test of Prime Minister Nikol Pashinyan's efforts to forge peace with longtime foe Azerbaijan.
Polls suggest Strong Armenia has the support of between six per cent and 11 per cent of the electorate, putting it in second place behind Pashinyan's ruling Civil Contract party, which has a substantial lead with between 24 per cent and 32 per cent.
Armenian civil society groups have raised alarm over what they allege are Russian state-sponsored disinformation efforts in the lead-up to the election.
Russian authorities routinely deny they meddle in other countries' internal affairs.
State media outlet Armenpress said the Central Election Commission had allowed investigators to initiate criminal proceedings against the six candidates, without going into further details.
Armenia's state Investigative Committee, which made the arrests, did not immediately respond on Saturday to questions about the reasons for the move.
There was no immediate response from Strong Armenia, which wants to maintain the country's economic and political ties to Russia, and has accused Pashinyan of stoking war with the Kremlin.
Armenia's interior ministry said earlier this week it had identified at least 78 cases of pre-election crimes and had detained 44 people, according to figures cited by Armenian media.
The reports did not specify which political parties the detained people belong to.
Pressure against Strong Armenia has been mounting ahead of Sunday's vote.
At an extraordinary session held late on Friday, the Central Election Commission rejected a lawsuit filed by another opposition group to ban Strong Armenia from participating in the elections over accusations it was bribing voters and financing its campaign illegally, among other issues.
Strong Armenia broadly dismissed the lawsuit, with Armenian media quoting the party's spokeswoman as saying the group was "ready for all scenarios" on Sunday.
