As of April 06, 2018 yes it's illegal, may be there is some new update. I'm not aware.
Here is the official circular from SBP
Prohibition of Dealing in Virtual Currencies/Tokens [State Bank of Pakistan] April 06, 2018
http://www.sbp.org.pk/bprd/2018/C3.htm
SBP prohibits financial sector from dealing in cryptocurrencies, says it will take action on violations. [Dawn] April 07, 2018
https://www.dawn.com/news/1399997
Pakistan bans cryptocurrencies. [Express Tribune] April 06,2018
https://tribune.com.pk/story/1679446/2-pakistan-bans-cryptocurrencies/
SBP doesn't make the laws in Pakistan. It can only prohibit financial institutions from touching crypto. In fact the SBP's ban is unconstitutional because one of the fundamental rights we enjoy is to be able to buy anything we like as long as it's legal. If we had decent sized exchanges they could have taken the SBP to court over the ban. Instead the only exchange we had folded overnight. In India they had large exchanges which took the matter to court and the government over there has had to re-evaluate their central bank's ban.