Police have previously described the suspect as an asylum seeker from Morocco who deliberately targeted women in the attack at a market square in the southwestern port of Turku on Friday, which left two people dead and eight injured.
The motive for the attack was still not known.
The Finnish intelligence agency SUPO said meanwhile that police authorities in southwestern Finland had received a tip early this year that Mechkah "had been radicalised and showed interest in extremist ideologies."
The tip, which had been forwarded to the SUPO, "contained no information about any threat of an attack."
Mechkah, whom police shot in the thigh while arresting him minutes after the rampage, is to appear before the Turku court on Tuesday via video link from hospital, the National Bureau of Investigation (NBI) said.
His court appearance had initially been scheduled for Monday.
Police will ask the court to remand him in custody on suspicion of two murders and eight attempted murders "with terrorist intent".
Investigators said Sunday that they had interrogated the suspect for the first time, but disclosed no information about the outcome.
Police will also request the detention of four other Moroccan citizens who were arrested in an overnight raid on a Turku apartment building and refugee housing centre just hours after the attack.
"They are suspected of participation in the murders and attempted murders committed with a terrorist intent. They deny any involvement in the offences," the NBI said.
Over 1,000 Tips
Police said earlier that the suspect was an asylum seeker who arrived in Finland in early 2016.
The attack occurred just after 4:00 pm (1300 GMT) on Friday, with police shooting the knife-wielding suspect minutes later.
The two people who died were both Finnish women, born in 1951 and 1986. Six of the injured were also women, while two men were injured trying to fend off the attacker.
Among the injured were an Italian, a Swede and a Briton.
Finland raised its emergency readiness level after the attack, increasing security at airports and train stations and putting more officers on the streets.
The SUPO said authorities had received over 1,000 tips in recent years similar to the one concerning Mechkah.
"Our aim is to investigate all tips, but in order to go through all of them we have to prioritise heavily. Those tips that contain information about a concrete threat must be prioritised," it said.
In June, the SUPO raised Finland's terror threat level by a notch, to "elevated" from "low", the second on a four-tier scale.
It said at the time that it saw an increased risk of an attack committed by Islamic State militants, noting that foreign fighters from Finland had "gained significant positions within IS in particular and have an extensive network of relations in the organisation."
The agency reiterated on Monday that it was closely watching around 350 individuals- an increase of 80 percent since 2012.
A minute of silence will be held across Finland on Sunday in honour of the victims.
Another minute of silence will be held in Helsinki today, organised by Christian and Muslim associations.
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