Ugandans will have to cough up 200 Ugandan shillings ($0.05) a day to use popular platforms like Twitter, Facebook and WhatsApp.
Museveni said he will sign the bill passed by the country's parliament once presented for his approval.
"Dear Uganda, I will not hesitate to sign the Social Media Bill into law once it lands on my desk. Social Media bill is seeking to tax every Ugandan using all social media platforms, Facebook, Twitter, Insta, WhatsApp on a daily basis," Museveni said in a tweet.
Parliamentary spokesman Chris Obore defended the law which comes into effect July 1, saying that as more Ugandans use social media it should become an important source of revenue for the country.
"The government is trying not to over rely on donor funding. It is just a redistributive tax as the government is out to look for money from those who have to finance projects," Obore told CNN.
He added: "The tax is very small. 200 shillings in Uganda to a dollar is very negligble. People in Uganda will not find it too expensive."
However, many Ugandans on social media see the tax as a government crackdown on free speech.
reported the tax would be implemented through mobile phone operators on individual SIM cards used to access social media.
@ntv #AmLiveNTV Uganda's action to tax social media is not only aimed at spread of fake news for fake news can be handled by court of law but just to limit people's freedom of expression in expressing evils by the leadership social media is live in most countries worldwide why ug— Samuel N Orutwa (@orutwasam) June 1, 2018