Old Testament
The Hebrew phrase wicked men, literally “Sons of Belial” is an expression rendered literally in older English Bibles so for example:
Certain men, the children of Belial, are gone out from among you, and have withdrawn the inhabitants of their city, saying, Let us go and serve other gods, which ye have not known; (Deuteronomy 13:3 KJV)
“Count not thine handmaid for a daughter of Belial” (1 Samuel 1:16 KJV)
The King James Version has the same phrase in Judges 19:22, 20:13, 1 Samuel 2:12, 10:27, 25:17, 25:25, 30:22, 2 Samuel 16:7, 20:1, 23:6, 1 Kings 21:13, 2 Chronicles 13:7, that is 16 out of the 27 times the phrase occurs. Those 16 times are all in the histories. However from Job to Nahum the KJV reverts to simply “ungodly” or “wicked” for the remaining 11 instances of the word.
The Greek Septuagint Old Testament likewise translates as “wicked men” (ἄνδρες παράνομοι) etc., as do most modern English translations.
New Testament
The only case in the Bible where Belial appears a name is 2Co 6:15:
And what concord hath Christ with Belial? or what part hath he that believeth with an infidel? (KJV)
And here the word in the Greek text is exactly that ‘Belial’ (Βελιάρ or Βελίαλ), similar to the way Jesus personalizes riches as “Mammon” in the sermon on the mount (Matthew 6:24) and again three times in the parable of the embezzling steward (Luke 16:9, 11, 13). Mammon does not exist as a demon of money, in the same way Belial does not exist as a named figure in the way that Satan exists from the time of Zechariah 3 and Job 1.
Belial is largely unknown as an actual character pre-Paul other than the 72 references found in the Dead Sea Scrolls, some of which appear to be meant literally, as a demon. Belial is also the name of one of the fallen angels in the Book of Jubilees, one of several versions of the angels that sinned story popular at this period.
But the context in 2 Corinthians 6:5, friendship with the world, does not suggest that Paul is using the term ‘Belial’ to mean ‘Satan’. If he were then why not use ‘Satan’?
Also given the use of ‘Belial’ in the Old Testament is so clearly not the same as the use of ‘Satan’ in Zechariah 3 and Job 1, the 2 Corinthians 6 reference lacks the precedent of a character as appears in those two Old Testament books.
In conclusion there’s not much reason to think that Paul meant anything more supernatural with ‘Belial’ than Christ meant with ‘Mammon’.