Research among 700 company directors found almost half were confident about prospects for their own company.
The Institute of Directors (IoD) said its survey revealed that worries about trade were not among the main three concerns for the first time since Brexit withdrawal negotiations started.
Optimism is now higher than at any time since the Prime Minister triggered Article 50 last March, said the IoD.
Tej Parikh, senior economist at the IoD, said: "After nearly a year of economic pessimism winning out among business leaders, the scales have tipped gently into the positive.
"It seems likely that meaningful progress in Brexit negotiations since December has brought some much needed reassurance.
"We urge the Government to provide further detail on its proposals for the UK's future trading and regulatory relationship with the EU, and to iron out its initiatives to narrow the skills gap and enhance business productivity through the Industrial Strategy.
"While directors' economic confidence has edged into positive territory, there's still plenty keeping them on the fence. Positivity has been held back by rising labour shortages and the burden of complying with Government regulations, and this should remind us that Brexit isn't the only game in town."