They found that targeting a part of the brain called the parietal lobe improved the ability of volunteers to solve numerical problems.
They hope the discovery could help people with dyscalculia, who may struggle with numbers.
Another expert said effects on other brain functions would need checking.
The findings are reported in the journal Current Biology.
Some studies have suggested that up to one in five people have trouble with maths, affecting not just their ability to complete problems but also to manage everyday activities such as telling the time and managing money.
Neuroscientists believe that activity within the parietal lobe plays a crucial role in this ability, or the lack of it.
When magnetic fields were used in earlier research to disrupt electrical activity in this part of the brain, previously numerate volunteers temporarily developed discalculia, finding it much harder to solve maths problems.
The latest research goes a step further, using a one milliamp current to stimulate the parietal lobe of a small number of students.
The current could not be felt, and had no measurable effect on other brain functions.
As it was turned on, the volunteers tried to learn a puzzle which involved substituting numbers for symbols.
Those given the current from right to left across the parietal lobe did significantly better when given, compared to those who were given no electrical stimulation.
The direction of the current was important - those given stimulation running in the opposite direction, left to right, did markedly worse at these puzzles than those given no current, with their ability matching that of an average six-year-old.
The effects were not short-lived, either. When the volunteers whose performance improved was re-tested six months later, the benefits appear to have persisted.
There was no wider effect on general maths ability in either group, just on the ability to complete the puzzles learned as the current was applied.
Dr Cohen Kadosh, who led the study, said: "We are not advising people to go around giving themselves electric shocks, but we are extremely excited by the potential of our findings and are now looking into the underlying brain changes.
"We've shown before that we can induce dyscalculia, and now it seems we might be able to make someone better at maths, so we really want to see if we can help people with dyscalculia.
By Fergus WalshMedical correspondent, BBC News
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"Electrical stimulation is unlikely to turn you into the next Einstein, but if we're lucky it might be able to help some people to cope better with maths."
Dr Christopher Chambers, from the School of Psychology at Cardiff University, said that the results were "intriguing", and offered the prospect not just of improving numerical skills, but having an impact on a wider range of conditions.
He said: "The ability to tweak activity in parts of the brain, turning it slightly 'up' or 'down' at will, opens the door to treating a range of psychiatric and neurological problems, like compulsive gambling or visual impairments following stroke."
However, he said that the study did not prove that the learning of maths skills was improved, just that the volunteers were better at linking arbitrary numbers and symbols, and he warned that researchers needed to make sure other parts of the brain were unaffected.
"This is still an exciting new piece of research, but if we don't know how selective the effects of brain stimulation are then we don't know what other brain systems could also be affected, either positively or negatively."
Sue Flohr, from the British Dyslexia Association, which also provides support for people with dyscalculia, said the research was welcome.
She said: "It's certainly an under-recognised condition, but it can ruin lives.
"It makes it very hard to do everyday things like shopping or budgeting - you can go into a shop and find you've spent your month's money without realising it."
Applying a tiny electrical current to the brain could make you better at learning maths, according to Oxford University scientists.