The economic climate indicator, which measures business confidence, stood at plus 0.3 in January, up from 0.2 the previous month and resuming its rise after two months of declines. The index turned positive in May 2014 - the month Lisbon exited an international bailout.
The National Statistics Institute also said its consumer confidence indicator was at a negative reading of 21.9 in January - its highest since May 2002 - compared with 22.3 in December.
The indices started rebounding at the start of 2013, when Portugal began to recover from its debt crisis which led to the worst economic slump since the 1970s. The economy is expected to have grown last year for the first time since 2010.